Imidazolium-based room-temperature ionic liquids, polymers, monomers and membranes incorporating same

ABSTRACT

The present invention provides gels, solutions, films, membranes, compositions, and other materials containing polymerized and/or non-polymerized room-temperature ionic liquids (RTILs). These materials are useful in catalysis, gas separation and as antistatic agents. The RTILs are preferably imidazolium-based RTILs which are optionally substituted, such as with one or more hydroxyl groups. Optionally, the materials of the present invention are composite materials comprising both polymerized and non-polymerized RTILs. The RTIL polymer is formed from polymerized RTIL cations typically synthesized as monomers and polymerized in the presence of the non-polymerized RTIL cations to provide a solid composite material. The non-polymerized RTIL cations are not covalently bound to the cationic polymer but remain as free cations within the composite material able to associate with charged subunits of the polymer. These composite materials are useful in catalysis, gas separation, and antistatic applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Nos.61/228,699, filed Jul. 27, 2009, and 61/228,433, filed Jul. 24, 2009,which are hereby incorporated by reference in their entirety to theextent not inconsistent with the disclosure herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with U.S. government support under grant numberW911NF-07-1-0115 awarded by the U.S. Army Research Office and undergrant DoD ARO HDTRA1-08-1-0028 awarded by the Department of Defensethrough the Defense Threat Reduction Agency. The U.S. government hascertain rights in the invention.

BACKGROUND OF THE INVENTION

Room-temperature ionic liquids (RTILs) are organic salts that are liquidat or below 100° C., and are composed entirely of cations and anions(i.e., free of any additional solvents) (Welton, Chem. Rev. 1999, 99:2071-2083; and Welton, Coord. Chem. Rev. 2004, 248:2459-2477). They haveattracted broad interest as novel solvents and liquid media for a numberof applications because they have a unique combination of liquidproperties. They have very low volatility, relatively low viscosity,high thermal stability, low flammability, high ionic conductivity,tunable polar solvation and transport properties, and in some cases,even catalytic properties. These characteristics have made RTILsexcellent candidates as environmentally benign solvents to replaceconventional organic solvents in many chemical, electrochemical, andphysical extraction/separation processes. In addition, RTILs have beenshown to be novel gas separation media in supported liquid membranes(SLMs) and novel catalysts in a number of chemical processes, withperformance enhancements in both cases due to the unique properties ofRTILs (Scovazzo et al. “Supported Ionic Liquid Membranes and FacilitatedIonic Liquid Membranes,” ACS Symposium Series 818 (Ionic Liquids), 2002,69-87; and Schaefer et al. “Opportunities for Membrane SeparationProcesses using Ionic Liquids,” ACS Symposium Series 902 (Ionic LiquidsIIIB: Fundamentals, Progress, Challenges, and Opportunities), 2005,97-110).

The use of RTILs on polymer supports for membrane applications hasprimarily been studied for catalysis and gas separations (Riisager andFehrmann, Ionic Liquids in Synthesis (2nd ed), Wiley-VCH: Weinheim,Germany, 2007; 527-558; Scovazzo et al., J. Membr. Sci. 2004; 238:57-63; and Jiang et al., J. Phys. Chem. B. 2007; 111: 5058-5061). RTILscan selectively permeate one gas over another (for example, CO₂/CH₄,CO₂/N₂, and SO₂/CH₄) or separate products from a reaction mixture suchas during a transesterification reaction (Hernandez-Fernandez et al., J.Membr. Sci. 2007; 293: 73-80). Employment of supported ionic liquidmembranes (SILMs) is attractive as RTILs possess negligible vaporpressures and can be impregnated into porous supports withoutevaporative losses, a hindrance for traditional supported liquidmembranes (SLMs). However, regardless of the nature of the liquid in thesupport (RTILs or others) the SLM configuration can fail if the pressuredifferential across the membrane is great enough to overcome theliquid-support interactions and push the liquid through the pores of thesupport. While there are certainly a multitude of research applicationswhere this pressure differential is not an issue, many industrial gasseparations occur at much higher pressures than SLMs can withstand,typically only a few atmospheres (Baker, Ind. Eng. Chem. Res. 2002; 41:1393-1411). In their current forms, SILMs are a more valuable tool forevaluating gas solubility, diffusivity, and separations in RTILs ratherthan a viable technology for industrial membrane separations (Fergusonet al., Ind. Eng. Chem. Res. 2007; 46: 1369-1374).

However, the idea of encapsulating RTILs in polymers and polymermembranes is not without merit. RTILs may be useful as non-volatileadditives for improving polymer processing and properties (Winterton, J.Mater. Chem. 2006; 16: 4281-4293). RTILs could be better stabilized inpolymer gas separation membranes if the support matrix is designed toprovide enhanced interactions with RTILs. A number of different supportshave been used in the study of SILMs for use as gas separationmembranes, yet none of these polymers truly resembles the RTILsthemselves (Ilconich et al., J. Membr. Sci. 2007; 298: 41-47). While theweak interactions between the RTILs and supports allow for gas diffusionas if it were a neat liquid, this configuration will inherently havelimitations to the pressure differential that can be applied.Researchers in conductive polymers and liquid crystals (LCs) have givena good deal of consideration to composite structures where free RTILsare contained within the polymer or LC matrix (Ohno, Macromol. Symp.2007; 249/250: 551-556; Nakajima et al., Polymer 2005; 46: 11499-11504;Yoshio et al., Mol. Cryst. Liq. Cryst. 2004; 413: 2235-2244; and Yoshioet al., J. Am. Chem. Soc. 2006; 128: 5570-5577).

Research in recent years of RTILs as selective gas separation media hasfocused primarily on CO₂-based separations, with SO₂ removal alsoappearing to be a promising pursuit (Jiang et al., Phys. Chem. B 2007,111: 5058; Huang et al., Chem. Commun. 2006, 38:4027; and Anderson etal., J. Phys. Chem. B 2006, 110: 15059). RTILs, especially those basedon imidazolium cations, exhibit an affinity for CO₂ relative to CH₄ andN₂. CO₂/CH₄ separation is of critical importance to natural gasprocessing and improving fuel quality. CO₂/N₂ separation from flue gasstreams (CO₂ capture and sequestration) is an issue currently garneringsignificant global attention (Bara et al., Acc. Chem. Res. 2010,43:152-159). RTILs have been proposed as alternative “green” solvents toreplace the volatile organic compounds (VOCs) typically employed in CO₂scrubbing (Baltus et al., Sep. Sci. Technol. 2005, 40: 525; and Anthonyet al., Int. J. Environ. Technol. Manage. 2005, 4: 105).

Several different approaches have been employed to exploit the desirableproperties of RTILs for gas separation applications. Many experimentshave focused on measuring the solubility of various gases of interest inRTILs at a range of pressures. The larger solubility of CO₂ compared toCH₄ and N₂ could perhaps be utilized to achieve separation throughpressure swing absorption. CO₂ could be selectively absorbed into theRTIL solvent, while the less soluble gas is swept away, creating aCO₂-lean stream. CO₂ could then be desorbed from solution to produce aCO₂-rich stream. This type of configuration appears more viable in RTILsthan in traditional VOCs, as there is little risk of volatilizing RTILsin the desorption step. An inherent drawback of such a pressure swingconfiguration with RTILs is that the volume of solvent required isdirectly proportional to the volume of gas to be processed and inverselyproportional to the concentration (partial pressure) of CO₂ in the feedstream. As the largest solubility of CO₂ in some common,imidazolium-based RTILs is ca. 0.08 mol L⁻¹ atm⁻¹ (2.2 cm³ (STP) cm⁻³atm⁻¹) at 40° C.; it becomes apparent that large volumes of RTILs wouldbe required to process large volumes of low pressure CO₂ from flue gasstreams.

Supported ionic liquid membranes (SILMs) have been examined as a meansto process CO₂ in a selective RTIL medium without the need for largevolumes of fluids (Scovazzo et al., J. Membr. Sci. 2004, 238: 57). SILMscan be prepared by “wetting” a porous polymer (or inorganic) supportwith an RTIL of interest. The volume of gas that can be processed isdirectly proportional to the membrane surface area and the feedpressure. Some SILMs exhibit ideal (i.e., single gas) CO₂ permeabilityapproaching 1000 barrers and ideal separation factors for CO₂/N₂ up to60 or higher. When viewed on a “Robeson plot”, these data indicate thatSILMs are highly competitive with polymer membranes and may be anindustrially attractive technology for CO₂/N₂ separations. SILMs do notappear as viable in CO₂/CH₄ separations when examined on a “Robesonplot” for that separation (Camper et al., Ind. Eng. Chem. Res., 2006,45: 6279; Robeson, L. M., J. Membr. Sci. 2008, 320: 390; and Robeson L.M., J. Membr. Sci. 1991, 62:165-185).

However, as a gas separation membrane platform, SILMs are not withouttheir own drawbacks. In many supports, weak capillary forces hold theRTIL within the matrix. While the lack of strong RTIL-supportinteractions allows for high gas permeability through the liquid phase,this also negatively impacts the stability of the SILM configuration.The transmembrane pressure differentials that SILMs can withstand appearlimited to a few atmospheres, before the RTIL is “squeezed” from thesupport. The long-term integrity of the support, especially those thatare polymer-based, is also of concern.

There are several reports of imidazolium-based room temperature ionicliquids (RTILs) containing primary, secondary, and tertiaryalcohol-functionalized cations (Holbrey et al., Green Chem. 2003, 5,731-736; Camper et al., Ind. Eng. Chem. Res. 2008, 47, 8496-8498;Boesman et al., Monatschefte für Chemie 2007, 138, 1159-1161; and Arnoldet al., C. Chem. Commun. 2005, 1743-1745). The primary alcoholfunctionality has been shown to influence the miscibility ofimidazolium-based RTILs with 1° and 2° alkanolamines (Camper et al.,Ind. Eng. Chem. Res. 2008, 47, 8496-8498). However, RTILs containing avicinal diol on the cation are much less common, although they have beenused as aldehyde protecting groups and ligands for Pd catalysis (Cai etal., Chin. Chem. Left. 2007, 18, 1205-1208; and Cai et al., Catal.Commun. 2008, 9, 1209-1213). The vicinal diol-functionalized RTILs usedin these studies employed the PF₆ anion, which has the liability ofhydrolyzing and generating HF under certain conditions (Cai et al.,Catal. Commun. 2008, 9, 1209-1213; and Visser et al., Ind. Eng. Chem.Res., 2000, 39, 3596-3960). Polymerizable imidazolium-based RTILs havebeen reported with bis(trifluoromethansulfonimide) anions andimidazolium-based cations containing a polymerizable styrene group and an-alkyl chain, an oligo(ethylene glycol) linkage or a nitrile terminatedn-alkyl chain (Bara et al., Polym. Adv. Technol., 2008, 19, 1415-1420;and Bara et al., Ind. Eng. Chem. Res., 2008, 47(24), 9919-9924).

RTIL polymers and materials of the present invention also show promiseas antistatic agents and materials. An antistatic agent is a compoundused for treatment of materials or their surfaces in order to reduce oreliminate buildup of static electricity. Its role is to make the surfaceor the material itself slightly conductive, either by being conductiveitself, or by absorbing moisture from the air and relying on theconductivity of water for charge dissipation.

Electrostatic charge buildup is responsible for a variety of problems inthe processing and use of many industrial products and materials (U.S.Pat. No. 6,592,988). Electrostatic charging can cause materials to sticktogether or to repel one another, which is particularly problematic infiber and textile processing. In addition, static charge buildup cancause objects to attract unwanted particles such as dirt and dust. Amongother things, this can decrease the effectiveness of fluorochemicalrepellents. Sudden electrostatic discharges from insulating objects canalso be a serious problem. With photographic film, such discharges cancause fogging and the appearance of artifacts. When flammable materialsare present, such as in high oxygen environments, a static electricdischarge can serve as an ignition source, resulting in fires and/orexplosions. Static buildup is a particular problem in the electronicsindustry, where electronic devices can be extremely susceptible topermanent damage by static electric discharges. Typical antistaticadditives contain functional groups able to conduct electrical chargesand include ethoxylated amines, fatty acids or esters, glycerol monostate, quaternary amines, and ionomers such as methacrylicacid/ethylene/NaI ionomers.

However, conventional antistatic materials have generally not been veryeffective in combination with fluorochemical repellents and often resultin degradation of the antistatic characteristics, and undesirableerosion or interactions with the treated substrate material. Forexample, amines, ethoxylated amines and quaternary amines can becorrosive to polycarbonate substrates and metals on electroniccomponents. Furthermore, it has been particularly difficult to combineconventional antistatic materials and fluorochemical repellents inpolymer melt processing applications, as, for example, the waterassociated with humectant antistatic materials vaporizes rapidly at meltprocessing temperatures. This has resulted in the undesirable formationof bubbles in the polymer and has caused screw slippage in extrusionequipment. Many antistatic materials also lack the requisite thermalstability, leading to thermal degradation of the material. Thus, thereremains a need in the art for antistatic agents that can be effectivelycombined to impart both good antistatic characteristics and arecompatible to a wider range of substrates.

SUMMARY OF THE INVENTION

This invention is in the field of gels, solutions, films, membranes,compositions and other materials containing polymerized and/ornon-polymerized room-temperature ionic liquids (RTILs). These materialsare useful in catalysis, gas separation and as antistatic agents.Preferably, the RTILs are imidazolium-based RTILs which are optionallyfunctionalized. In some embodiments, the materials of the presentinvention are composite materials comprising both polymerized andnon-polymerized RTILs.

A. Compositions Using Diol-Functionalized, Imidazolium-Based RTILs

Functionalized RTILs are useful as liquid-phase reaction and transportmedia in a number of important application areas including catalysis,gas separations, and removal of heavy metals from water. In differentaspects, the invention provides diol-functionalized imidazolium-basedRTILs and polymerizable RTILs, aqueous solutions containing the RTILs ofthe invention, membranes and other polymeric materials formed from theRTILs of the invention and methods for making and using the RTILS of theinvention.

In one aspect, the invention provides salts with abis(trifluoromethansulfonimide) (Tf₂N) anion and an imidazolium-basedcation. In an embodiment, the cation is a substituted imidazolium-basedheterocycle with substituents at both nitrogen atoms of thefive-membered ring. Substituents may also be present at one or more ofthe carbon atoms of the ring. In an embodiment, one of the nitrogens inthe ring is attached to a group including a vicinal diol group. Asreferred to herein, a vicinal diol group refers to a group in which analcohol group is bonded to each of two adjacent carbon atoms in amolecule.

In an embodiment, the salt may be described as including at least threegroups (R₁-R₃) attached to the imidazolium ring. In an embodiment, groupR₁ includes the vicinal diol group and is attached to one of thenitrogen atoms in the ring, R₂ is attached to the carbon between thenitrogen atoms and R₃ is attached the other nitrogen atom in the ring.R₂ may be hydrogen, while R₁ and R₃ are other than hydrogen. In anembodiment, R₃ is alkyl with the number of carbon atoms between 1 and10. In different embodiments, R₃ may be methyl (Me), ethyl (Et), propyl(Pr), butyl (Bu), or benzyl (Bn). In different embodiments, R₂ may behydrogen or methyl. Formula 1 illustrates a structure where R₁ is equalto CH₂CHOHCH₂OH.

In another aspect, the invention provides a method for synthesizing thewater-miscible salts. In one embodiment, the groups attached to theimidazolium ring are selected so that the salt is miscible in water. Asused herein, a salt is miscible in water when it is capable of beingmixed with water in all proportions without separate phases forming. Inan embodiment, R₁ is as shown in Formula 1, with R₂ being hydrogen andR₃ being selected from methyl or ethyl. In another embodiment, R₂ may behydrogen or methyl and R₃ may comprise an alcohol group, an amine group,or a nitrile group. In another embodiment, R₂ may be hydrogen or methyland R₃ may comprise carboxylic acid, sulfonic acid/sulfonate,carbohydrate, poly(ethylene glycol) (PEG), benzyl or a substitutedbenzyl derivative.

In another embodiment, R₃ may comprise a polymerizable group. Indifferent embodiments, the polymerizable group may be a vinyl or styrenegroup. Formula 2 illustrates a structure of a vinyl imidazolium-basedmonomer (R₂ is hydrogen, R₃ is CHCH₂), while Formula 3 illustrates astructure of a styrene imidazolium-based monomer (R₂ is hydrogen, R₃ isCH₂PhCHCH₂).

In another embodiment, the present invention provides polymers andpolymer membranes comprising a plurality of diol-functionalizedimidazolium repeating units, the repeating unit being described by thegeneral formula:

where X⁻ is an anion selected from the group consisting of abistrifluoromethylsulfonyl)imide ion (Tf2N⁻), a halide ion, ahexafluorophosphate ion (PF₆ ⁻), a tetrafluoroborate ion (BF₄ ⁻), adicyanamide ion (N(CN)₂ ⁻), a sulfonated ion and a fluorinatedsulfonated ion. In a further embodiment, X⁻ is Tf2N⁻. Suitable halidesinclude, but are not limited to Cl⁻, Br⁻, I⁻. Suitable sulfonatesinclude, but are not limited to mesyalte, triflate, and tosylate. Themembrane optionally further comprises repeating crosslink units and theratio of crosslink repeating units to diol-functionalized imidazoliumrepeating units is greater than zero and less than or equal to 5%. In afurther embodiment, the present invention provides a composite membranecomprising a porous support where the diol-functionalized imidazoliumpolymer is embedded within the pores of the support. In anotherembodiment, the porous support is a polymeric porous support, such as apolysulfone support. In an embodiment, the thickness normalized watervapor flux of the membrane is from 100 kg m⁻² day⁻¹ μm to 200 kg m⁻²day⁻¹ μm.

In another aspect, the invention provides a solution comprising waterand the water-miscible imidazolium-based cation Tf₂N anion salts of theinvention. In an embodiment, the salts are water-miscible at roomtemperature. In an embodiment, the solution is homogeneous. Thepercentage (by volume) of the salt in the solution may be 10% to 90%,20% to 80%, 25% to 75%, 30% to 70%, or 40% to 60%. The solution may alsocomprise species which can play an active part in a separation process.Such active species include but are not limited to amines includingalkanolamines that are widely used for the removal of CO2, H₂S and other“acid” gases from natural gas (CH₄), flue gas from the exhaust ofcombustion processes, synthesis gas (“syngas” CO/H₂ mixtures) and otherindustrial gas mixtures. Amines may be combined with the salts with orwithout water in similar proportions to those described above. Otheractive species include inorganic salts and other RTILs.

In another aspect, the invention provides a method for synthesizing thewater-miscible salts of the invention. In an embodiment, the methodcomprises the steps of forming a Cl⁻ salt of the desired cation and thenion exchanging the Cl⁻ salt with a Tf₂N⁻ salt in an organic solvent orwater. In an embodiment, the Cl⁻ salt of the desired cation can beprepared in a neat (solvent free) reaction. Because this first step canbe conducted without the use of organic solvents and without workupsteps, this first step of the process can be considered an improvementover conventional reactions of this type. In an embodiment, the Cl⁻ saltof the desired cation can be prepared by stirring1-chloro-2,3-propanediol with the corresponding imidazole reagent whileheating (see Scheme 1, where R′ is equivalent to R₂ and R is equivalentto R₃). In an embodiment, the Tf₂N⁻ salt used in the ion exchange stepis selected to have low solubility in the organic solvent. In anembodiment, the salt is KTf₂N. In an embodiment, the organic solvent isCH₃CN. Typically, the final products will be isolated by filtering thebyproducts and evaporating the solvent. The final products can bepurified by dissolving in methanol and stirring with activated carbon orby column chromatography. The product is isolated by filtration and thenconcentrated.

In another aspect, the invention provides salts or polymerizable saltswith anions other than Tf₂N. In an embodiment, the cation is as shown inFormula 2 or 3 with the anion being tetrafluoroborate BF₄ ⁻, dicyanamideN(CN)₂ ⁻, hexafluorophosphate (PF₆—), C(CN)₃ ⁻, B(CN)₄ ⁻, N(SO₂F)₂ ⁻,SbF₆ ⁻, Cl⁻, Br⁻, I⁻, alkyl sulfonate (R—SO₃ ⁻) and other sulfonates(such as mesylate, tosylate, etc). Salts with bromine anions would bemade similarly to salts with chlorine anions, except that chloride isreplaced with bromide on the electrophile. Other salts can be preparedby ion exchange in water or other solvents. Anion-exchange can beachieved using alkali metal or ammonium salts of these anions.

In an embodiment, any of the polymerizable salts of the invention may bepolymerized into the form of a thin film. In an embodiment, the filmthickness is from 50 nm to 200 micrometers. Such a poly(RTIL) film maybe used as a membrane for separations.

In another embodiment, the polymerizable salts of the invention may bepolymerized in the presence of a non-polymerizable RTIL to form acomposite membrane. Composite membranes have been detailed in Bara etal., Polym Adv. Technol. 2008. A variety of RTILs can be employed insuch membranes, including commercial ionic liquids and custom madefunctionalized RTILs.

B. Compositions Comprising Polymerized and Unpolymerized RTILs

Another aspect of the present invention provides compositions andcomposite materials, such as membranes and films, comprising RTILs incombination with non-polymerized RTILs. The polymer is formed frompolymerized RTIL cations typically synthesized as monomers andpolymerized in the presence of the non-polymerized RTIL cations toprovide a solid composite material. The non-polymerized RTIL cations arenot covalently bound to the cationic polymer but remain as free cationswithin the composite material able to associate with charged subunits ofthe polymer. The solid composite material may further contain unboundnegatively charged anions which are able to associate with positivecharges on the polymer or positively charged non-polymerized RTILs.These composite materials are useful in catalysis, gas separation and asantistatic materials.

Polymerized RTILs of the present invention, also referred to herein as“poly(RTIL)s”, primarily comprise RTIL cations attached to a polymerbackbone. The polymer backbone can be any suitable polymer backboneknown in the art, including but not limited to, poly(acrylate) orpoly(styrene) backbones. Polyanions such as poly(styrene sulfonic acidsalts) have also been employed, along with poly(zwitterions) andcopolymers. In one embodiment, two distinct polymer architectures areused to interface with non-polymerized free RTIL cations. The firstarchitecture is a side-chain configuration (Formula 4a) and the second amain-chain or ionene configuration (Formula 4b):

Both types of polymers shown in Formulas 4a and 4b can be utilized withimidazolium-based RTILs or other RTIL cations to form homogeneous, solidcomposites that do not phase separate. Composite materials comprisingpolymerized RTILs with unpolymerized RTIL, also referred to herein as“poly(RTIL)-RTIL”, contain up to approximately 60 mol % non-polymerizedRTIL cations that remain unbound to the polymer chain are readilyfabricated.

Polymers of Formula 4a can be swollen with RTILs or other organicsolvents before or after polymerization. When employed as a thin film,they may be used as selective membranes. There are no reports in theliterature of incorporating non-polymerized RTILs within a polymerizedRTIL membrane to enhance transport or capture of a gas. Optionally, thecomposites of the present invention further include additional transportagents and capture agents within the composite material in addition tothe non-polymerized RTILs. Examples of facilitated transport agentsinclude: Co²⁺ and complexes (especially including imidazole-Co²⁺compounds) for O₂, amines for CO₂, Ag⁺ and complexes for olefins (i.e.ethylene, propylene, etc.). Capture agents include strong bases such asOH⁻ for CO₂, SO₂, H₂S or strong acids such as H⁺ for NH₃. These agentsmay or may not be designed to be tethered to an RTIL so as to enhancetheir compatibility with the polymer backbone.

RTIL cations useful as polymerized and non-polymerized RITL cations ofthe present invention include, but are not limited to, organic cationssuch as imidazolium, pyridinium, pyrrolidinium, ammonium, and sulfoniumions. The polymerized monomer RTIL cations may be the same or differentcatioris as the non-polymerized RTIL cations. Preferably, the RTILcation is an imidazolium cation. In one further embodiment, the cationis selected from group consisting of 1-alkyl-3-methylimidazolium,1-alkylpyridinium, and N-methyl-N-alkylpyrrolidinium ions. In oneexample, 1-butyl-3-methylimidazolium tetrafluoroborate, or [bmim][BF₄],is used with an imidazole skeleton to form a colorless liquid with highviscosity at room temperature with a melting point of about −80° C.

In one embodiment, the composite material has the general formula:

where RTIL⁺ is a non-polymerized room-temperature ionic liquid cation, nis an integer from 2 to 10,000, X⁻ is an anion, L is a spacer or linkinggroup which connects two rings, and Y₁ and Y₂ are independently of eachother a hydrophobic tail group attached to each ring and having 1 to 20carbon atoms and optionally comprises a polymerizable group. Each spacerL is attached to a first nitrogen atom in each of the two linked rings.The attachment may be through a covalent or a non-covalent bond such asan ionic linkage. Each hydrophobic tail group Y is attached to thesecond (other, non-bridged) nitrogen atom in each ring. Hydrophobictails may also be attached to one or more carbon atoms of the ring.

In a further embodiment, the composite material has the general formula:

where Z₁ through Z₆ are individually selected from the group consistingof hydrogen and hydrophobic tail groups, RTIL⁺ is a non-polymerizedroom-temperature ionic liquid cation, n is an integer from 2 to 10,000,X⁻ is an anion, L is a spacer or linking group which connects two rings,and Y₁ and Y₂ are independently of each other a hydrophobic tail groupattached to each ring and having 1 to 20 carbon atoms and optionallycomprises a polymerizable group. In an embodiment, the hydrophobic tailgroup has between one and 12 carbon atoms and optionally comprises apolymerizable group. Attachment of a hydrophobic tail to one or morecarbon atoms in the ring in addition to the hydrophobic tail attached tothe nitrogen can be used to tune phase structure and curvature.

In one embodiment, the main chain polymer comprises imidazolium-basedionenes and composites. Formula 7 shows imidazolium-based ionenes(Formula 7a), and an imidazolium-based ionene capable of forming a gelwith various solvents (Formula 7b):

Imidazolium based ionenes (Formula 7a) may be synthesized frombis(imidazole) compounds. These polymers are capable of forming stablecomposites with imidazolium-based RTILs and mixtures of RTILs withactive agents. Furthermore, ionenes of Formula 7b are capable of forminga gel with water, alcohols, and other organic solvents.

Initial testing also suggests that these polymers may be useful as gasseparation membranes, selective for CO₂ and/or H₂ relative to N₂ and CH₄(see FIGS. 1-4). Additionally, these and other ionenes may besynthesized by a unique method. Typically, the polymers shown in Formula7a are synthesized from a bis(imidazole) and a di-functional molecule(alkyl dihalide, oligo(ethylene glycol) dihalide, etc.). Unfortunately,the use of tri-functional molecules or greater can produce star polymersand/or crosslinked systems. Typically, anion-exchange would be performedafter polymer growth was complete. However, if a salt containing thedesired anion is insoluble in the solvent of interest (e.g., KTf₂N inacetonitrile) the reactants may be dissolved in solution with thebis(imidazole) and difunctional monomer (typically dihalide orditosylate). Should the reaction produce a by-product that is insolublein the solvent of interest (e.g. KCl in acetonitrile), a precipitatewill be formed and the final polymer product will not require anionexchange. As many ionenes containing halides (and other anions) may beglassy in nature and hygroscopic and hydrophilic, anion exchange may bebeneficial to promote formation of a rubbery polymer and hydorphobicity.Furthermore, this mechanism can eliminate a processing step(ion-exchange) by performing it in situ, and improve polymer synthesisconditions, as certain ionenes will precipitate prematurely fromsolution before large polymer chains can be produced.

Ammonium-based ionenes (as well as phosphonium and others) may also beuseful to interface with RTILs. Ammonium-based ionenes are advantageousbecause many diamine starting materials are commercially available inlarge quantities. Ammonium-based ionenes are capable of formingcomposites with a variety of RTILs. These composites might also find usein antistatic applications, as well as in gas separation membranes andother applications mentioned herein. Synthesis of an ammonium-basedionene, followed by ion-exchange, and interfacing with imidazolium andammonium-based RTILs is shown in Scheme 1:

The polymerized RTIL materials disclosed above exhibit many propertiesdesired for improved antistatic materials. The polymerized RTILmaterials illustrated in Schemes 2 and 3 below can further be blendedwith imidazolium-based unpolymerized RTILs to form additional compositematerials having desirable properties.

In one embodiment, the present invention provides a compositioncomprising a polymerized imidazolium RTIL; and an unpolymerizedimidazolium RTIL where at least 5 mol % of the RTIL cations of thecomposite material remains unbound to the cationic polymer (i.e., areunpolymerized RTIL). In further embodiments, at least 10 mol % of theRTIL cations, at least 20 mol % of the RTIL cations, or at least 40 mol% of the RTIL cations of the composite material remains unbound to thecationic polymer. In one embodiment, between approximately 5 mol % andapproximately 60 mol % of the RTIL cations of the composite materialremains unbound to the cationic polymer. In further embodiments, betweenapproximately 10 mol % and approximately 50 mol %, or betweenapproximately 15 mol % and approximately 25 mol % of the RTIL cations ofthe composite material remains unbound to the cationic polymer.

In a further embodiment, the present invention provides a compositioncomprising:

a) a polymerized RTIL having the formula:

wherein,

-   -   R₁ and R₂, independently of one another, are selected from the        group consisting of branched and unbranched alkylene,        alkenylene, alkynylene and arylene groups having 1 to 20 carbon        atoms,    -   X₁ ⁻ is an anion,    -   Y₁ is selected from the group consisting of hydrogen and        branched and unbranched alkyl, alkenyl and alkynyl groups having        1 to 12 carbon atoms,    -   Z₁ and Z₂, independently of one another, are selected from the        group consisting of hydrogen and branched and unbranched alkyl,        alkenyl and alkynyl groups having 1 to 12 carbon atoms, and    -   n is an integer from 2 to 100,000; and

b) an unpolymerized RTIL having the formula:

wherein,

-   -   R₃ and R₄, independently of one another, are selected from the        group consisting of branched and unbranched alkyl, alkenyl,        alkynyl, and aryl groups having 1 to 20 carbon atoms,    -   X₂ ⁻ is an anion,    -   Y₂ is selected from the group consisting of hydrogen and        branched and unbranched alkyl, alkenyl, and alkynyl groups        having 1 to 12 carbon atoms,    -   Z₃ and Z₄, independently of one another, are selected from the        group consisting of hydrogen and branched and unbranched alkyl,        alkenyl, and alkynyl groups having 1 to 12 carbon atoms, and        wherein the unpolymerized RTIL is between 5 mol % to 60 mol % of        the total RTIL of the composition. In further embodiments, n is        an integer from 5 to 100,000, 10 to 100,000, 100 to 100,000, or        10 to 10,000.

Preferably, Y₁, Y₂, Z₁, Z₂, Z₃, and Z₄, independently of one another,are selected from the group consisting of hydrogen and branched andunbranched alkyl groups having 1 to 4 carbon atoms. Optionally, Y₁ andY₂ are hydrogen or methyl groups, and Z₁, Z₂, Z₃, and Z₄ are hydrogen.X₁ and X₂ may be the same or different anions.

In a further embodiment, R₁ and R₂, independently of one another, areselected from the group consisting of branched and unbranched alkylene,alkenylene, alkynylene, and arylene groups having 1 to 10 carbon atoms.Preferably, R₁ and R₂, independently of one another, are selected fromthe group consisting of branched and unbranched alkylene, and alkenylenegroups having 1 to 10 carbon atoms. In one embodiment, R₃ and R₄,independently of one another, are selected from the group consisting ofbranched and unbranched alkyl, alkenyl, alkynyl, and aryl groups having1 to 10 carbon atoms. Preferably, R₃, and R₄, independently of oneanother, are selected from the group consisting of branched andunbranched alkyl and alkenyl groups having 1 to 6 carbon atoms or 1 to 4carbon atoms. Optionally, at least one of R₃ and R₄ is a methyl group.Optionally, one or more carbon atoms in at least one of R₁, R₂, R₃, orR₄ is substituted. For example, at least one of R₁, R₂, R₃ or R₄contains one or more OH groups.

In a further embodiment, the polymerized RTIL of the composition has theformula:

In another embodiment, the present invention provides a compositioncomprising:

-   -   a) a polymerized RTIL comprising a plurality of RTIL-based        repeating units, the repeating unit being described by the        general formula:

-   -   wherein,    -   R₁ is selected from the group consisting of hydrogen and        branched and unbranched alkyl, alkenyl, alkynyl, and aryl groups        having 1 to 20 carbon atoms; R₂ is selected from the group        consisting of a bond, branched and unbranched alkylene,        alkenylene, alkynylene, and arylene groups having 1 to 12 carbon        atoms,    -   X₁ is an anion,    -   Z₁, Z₂ and Z₃, independently of one another, are selected from        the group consisting of hydrogen and branched and unbranched        alkyl, alkenyl, alkynyl, and aryl groups having 1 to 12 carbon        atoms, and    -   the number of repeating units in the RTIL polymer is from 2 to        100,000; and    -   b) an unpolymerized RTIL having the formula:

-   -   wherein,    -   R₃ and R₄, independently of one another, are selected from the        group consisting of branched and unbranched alkyl, alkenyl,        alkynyl, and aryl groups having 1 to 20 carbon atoms,    -   X₂ is an anion,    -   Y is selected from the group consisting of hydrogen and branched        and unbranched alkyl, alkenyl, and alkynyl groups having 1 to 12        carbon atoms,    -   Z₄ and Z₅, independently of one another, are selected from the        group consisting of hydrogen and branched and unbranched alkyl,        alkenyl and alkynyl groups having 1 to 12 carbon atoms, and        wherein the unpolymerized RTIL is between 5 mol % to 60 mol % of        the total RTIL of the composition. In further embodiments, the        number of repeating units in the RTIL polymer is from 5 to        100,000, 10 to 100,000, 100 to 100,000, or 10 to 10,000.

Preferably, Y, Z₁, Z₂, Z₃, Z₄, and Z₅, independently of one another, areselected from the group consisting of hydrogen and branched andunbranched alkyl groups having 1 to 4 carbon atoms. Optionally, Y ishydrogen or a methyl group, and Z₁, Z₂, Z₃, Z₄, and Z₅ are hydrogen. X₁and X₂ may be the same or different anions.

In the above embodiment, the repeating units can be linked togetherthrough the main carbon chain or additionally through cross-linkers. Infurther embodiments where the repeating units are linked togetherthrough the main carbon chain, the polymerized RTIL has the formula:

where n is an integer from 2 to 100,000, optionally from 5 to 100,000,10 to 100,000, 100 to 100,000, or 10 to 10,000.

In a further embodiment, the polymerized RTIL has the formula:

In one embodiment, R₂ is selected from the group consisting of a bond,branched and unbranched alkylene, alkenylene, alkynylene, and arylenegroups having 1 to 8 carbon atoms. When R₂ is a bond, it is understoodthat this bond is between the carbon atom of the polymer backbone andthe nitrogen atom of the imidazolium ring and that an additional atom isnot present. In a further embodiment, R₁, R₃, and R₄, independently ofone another, are selected from the group consisting of branched andunbranched alkyl, alkenyl, alkynyl and aryl groups having 1 to 10 carbonatoms. Preferably, R₁, R₃, and R₄, independently of one another, areselected from the group consisting of branched and unbranched alkyl andalkenyl groups having 1 to 6 carbon atoms or 1 to 4 carbon atoms.Optionally, at least one of R₃ and R₄ is a methyl group. Optionally, oneor more carbon atoms in at least one of R₁, R₃, or R₄ is substituted.For example, at least one of R₁, R₃, or R₄ contains one or more hydroxylgroups.

In a further embodiment, R₁ has the formula:

where n is 0, 1, 3, or 5;

where p is 1 or 2;

where n is 3 or 5; and

where L is an alkylene, or alkenylene group having 1 to 4 carbon atoms.In a further embodiment, R₁ is a diol in that it contains two hydroxylgroups. In a further embodiment, R₁ has the formula:

In further embodiments, the unpolymerized RTIL for these compositionshas the formula:

In typical embodiments, the composite material contains anions(represented by X⁻ in the above formulas) that are not chemically bondedto the main polymer chain and are able to associate with the polymerizedand non-polymerized charged RTIL cations. A wide range of anions can beemployed, from simple halide anions (i.e., chloride (Cl⁻), bromide(Br⁻), and iodide (I⁻) ions), which generally inflect high meltingpoints, to inorganic anions such as tetrafluoroborate BF₄ ⁻, dicyanamideN(CN)₂ ⁻, hexafluorophosphate (PF₆ ⁻), C(CN)₃ ⁻, B(CN)₄ ⁻, N(SO₂F)₂ ⁻,OTf⁻, SbF₆ ⁻, and to large organic anions like bistriflimide, mesyalte,triflate or tosylate. Ionic liquids with simple non-halogenated organicanions, such as formate, alkylsulfate, alkylphosphate or glycolate, canalso be used. In one embodiment, the compositions of the presentinvention contain bis(trifluoromethansulfonimide) (Tf₂N⁻) as the anion.

C. Formation of Films and Membranes Comprising RTIL Compositions

The polymerized RTIL and unpolymerized RTIL compositions describedherein are used to construct thin films and membranes. In oneembodiment, the films and membranes are constructed using a poroussupport. In an embodiment, the RTIL-based material (polymerized RTILcomposition or RTIL-based composite material) is embedded or locatedwithin the pores of a support. In the portions of the support containingthe RTIL-based material, the RTIL-based material fills enough of thepore space of the support so that separation process is controlled bythe RTIL-based material. In an embodiment, RTIL-based material ispresent throughout the thickness of the support, so that the thicknessof the composite membrane may be taken as the thickness of the support.During fabrication of the composite membrane, the monomer mixture may beapplied to only a portion of the surface of the support. The RTIL-basedmaterial may be retained within the support by mechanical interlockingof the RTIL-based material with the support.

In another embodiment, the RTIL-based material forms a layer on thesurface of the support; this layer acts as a membrane. In differentembodiments, the thickness of this layer is less than 10 microns, lessthan 5 microns, less than 2 microns, less than 1 micron, or less than0.5 micron. Optionally, the membrane or film has a thickness of lessthan 500 nanometers, less than 200 nanometers, or less than 150nanometers. In an embodiment, the polymerizable RTIL monomers may bepolymerized into the form of a thin film having a thickness from 50 nmto 200 micrometers.

In a further embodiment, the membrane or film comprises a first RTILpolymer layer and an opposing second RTIL polymer layer, where theunbound anions and unpolymerized RTIL cations are between the first andsecond RTIL polymer layers. Each polymer layer comprises polymerizedRTIL cations wherein the positively charged RTIL units of the polymerlayer face inward allowing ionic interactions to form between theunbound anions, unbound RTIL cations and polymerized RTIL cations.

In an embodiment, the porous support is hydrophilic. As used herein, ahydrophilic support is wettable by water and capable of spontaneouslyabsorbing water. The hydrophilic nature of the support can be measuredby various methods known to those skilled in the art, includingmeasurement of the contact angle of a drop of water placed on themembrane surface, the water absorbency (weight of water absorbedrelative to the total weight, U.S. Pat. No. 4,720,343) and the wickingspeed (U.S. Pat. No. 7,125,493). The observed macroscopic contact angleof a drop of water placed on the membrane surface may change with time.In different embodiments, the contact angle of a 2 μL drop of waterplaced on the support surface (measured within 30 seconds) is less than90 degrees, from 5 degrees to 85 degrees, zero degrees to thirty degreesor is about 70 degrees. In another embodiment, the membrane is fullywetted by water and soaks all the way through the membrane after aboutone minute. Hydrophilic polymeric supports include supports formed ofhydrophilic polymers and supports which have been modified to make themhydrophilic. In another embodiment, the support is hydrophobic.

In an embodiment, the porous support in this system is selected so thatthe diameter of the pores is less than about 10 microns. In differentembodiments, the support is microporous or ultraporous. In differentembodiments, the support has a pore size less than about 0.1 micron,from 0.1 micron to 10 microns, from 0.5 micron to 5 microns, or from 0.5to 1 micron. The characteristic pore size of the membrane may depend onthe method used to measure the pore size. Methods used in the art todetermine the pore size of membranes include Scanning ElectronMicroscopy analysis, capillary flow porometry analysis (which gives amean flow pore size), measurement of the bubble pressure (which givesthe largest flow pore size), and porosimetry.

The porous support membrane gives physical strength to the compositestructure. The support should also be thermally stable overapproximately the same temperature range as the RTIL membranes to beused.

The support is selected to be compatible with the monomer solution, aswell as to be compatible with the liquid or gas to be filtered. When themonomer solution and the support are compatible, the support isresistant to swelling and degradation by the monomer solution. In anembodiment, any organic solvent used in the solution and the support areselected to be compatible so that the support is substantially resistantto swelling and degradation by the organic solvent. Swelling and/ordegradation of the support by the solvent can lead to changes in thepore structure of the support.

The porous support may be made of any suitable material known to thoseskilled in the art including polymers, metals, and ceramics. In variousembodiments, the porous polymer support comprises polyethylene(including high molecular weight and ultra high molecular weightpolyethylene), polytetrafluoroethylene polyacrylonitrile (PAN),polyacrylonitrile-co-polyacrylate, polyacrylonitrile-co-methylacrylate,polysulfone (PSf), Nylon 6, 6, poly(vinylidene difluoride), orpolycarbonate. In an embodiment, the support may be a polyethylenesupport or a support of another polymer mentioned above (which mayinclude surface treatments to affect the wettability of the support). Inanother embodiment, the support may be a polysulfone support, an exampleof which is Supor® (Pall Inc, Ann Arbor, Mich.). The support may also bean inorganic support such as a nanoporous alumina disc (Anopore, JWhatman, Ann Arbor, Mich.). The porous support may also be a compositemembrane.

In an embodiment, the invention also provides methods for makingmembranes comprising polymerized RTILs or composites of polymerizedRTILs and unpolymerized RTILs. In an embodiment, the invention providesa method for making a composite membrane comprising the steps of:providing a porous support, preparing a monomer mixture comprising aplurality of polymerizable salts of the invention, and a polymerizationinitiator. In an embodiment, the mixture also comprises anonpolymerizable RTIL. In an embodiment, no cross-linking agent is used.In another embodiment, the monomer mixture may further comprise anoptional cross-linking agent molecule to help promote intermolecularbonding between polymer chains. In an embodiment, the cross-linkingagent is soluble in the solvents used to make the membranes and is not apolymer. In an embodiment, the cross-linking agent has less than 10monomeric repeat units and/or has a weight less than 500 Daltons.Typically, the cross-linking agent or curing agent is a small moleculeor monomeric cross linker such as divinyl benzene (DVB). Additionalcross-linking agents are known to those skilled in the art, includinggemini styrene and vinyl imidazolium crosslinkers (Bara et al., J.Membr. Sci. 2008; 316:186-191). In an embodiment, the maximum amount ofcross-linking agent is 10 wt % to 15 wt %. In an embodiment, the amountof cross-linking agent is greater than zero and less than or equal to 10mol % or greater than zero and less than or equal to 5 mol %.

Solvents useful in the preparation of RTIL membranes of this inventioncan be any solvent known in the art, including but not limited todichloromethane, acetonitrile and methanol, that is able to dissolve thedesired components. Preferably, any solvent used does not degrade orchemically change the components, or cause unwanted chemical reactions.

In an embodiment where the RTIL-based material is embedded into thesupport, a quantity of the monomer mixture is placed on a surface of theporous support membrane and then infused into the porous support. In oneaspect of the invention, the support is impregnated with the monomermixture using pressure to drive the monomer mixture into the pores ofthe support. In some instances, the monomer mixture and support may beheated to decrease the viscosity of the mixture before pressure isapplied. When pressure is applied, the LLC mixture and support membranemay be sandwiched between a pair of load transfer plates (e.g., glassplates). Additionally, a pair of polymeric sheets or a hydrophobiccoating on the plates may be used to facilitate release of the supportmixture and membrane from the load transfer plates. Suitable densepolymeric sheets that are transparent to UV or visible light include,but are not limited to, Mylar® (a biaxially-oriented polyester film madefrom ethylene glycol and dimethyl teraphthalate). The monomer mixtureneed not completely fill the pore space of the support, but fills enoughof the pore space of the support so that separation process iscontrolled by the pores of the RTIL-based material. In an embodiment,the monomer mixture is pushed uniformly through the entire supportmembrane thickness.

After impregnation of the support with the monomer mixture, the RTILmonomers are then polymerized. In an embodiment, the RTIL monomers canbe photo-crosslinked by exposure to UV light in the absence of oxygen atambient temperature. Other temperatures as known by those skilled in theart may be used during the cross-linking process. Other methods ofcross-linking as known to those skilled in the art may also be used. Forexample, thermal cross-linking may be performed using a cationicinitiator as a cross-linking agent. The degree of cross-linking can beassessed with infrared (IR) spectroscopy. In different embodiment, thedegree of polymerization is greater than 90% or greater than 95%.

In other embodiments, the RTIL-based material is formed as a thin,supported top-film on top of the support. In different embodiments, thecoating of the RTIL monomer mixture can be formed by solution-castingthe RTIL monomer mixture to make thin films on membrane supports afterevaporation of a delivery solvent; doctor-blade draw-casting; orroll-casting. It is preferred that that coating be free of surfacedefects such as pinholes and scratches. In one embodiment, a commercialfoam painting sponge or other such applicator can be used to apply thesolution to the support. In another embodiment, the solution can beapplied by roller casting. The amount of material on the support can becontrolled by the number of applications and the concentration of thecasting solution. If desired, more than one layer of solution may beapplied to the support to form multiple layers of the RTIL polymer andthereby control the film thickness. Some of the solution may penetrateinto the support, with the extent of penetration depending on the natureof the solution, the support, and the application process.

In an embodiment, the membranes of the invention comprise polymerizedRTIL monomers, the RTIL monomers comprising a vicinal diol group and apolymerizable group. In an embodiment, the RTIL monomers have astructure according to formula 2 or formula 3. In an embodiment, theas-synthesized monomer is purified before fabrication of the membrane.Additional purification techniques include, but are not limited to,removal of impurities with liquid-liquid extraction and stirring withactivated charcoal, dry column vacuum chromatography, and combinationsthereof. In an embodiment, the thickness-normalized to 1 μm water vaporflux as measured by evaporation into an environment with 1% humidity isgreater than 50 kgm⁻² day⁻¹ μm, from 75 to 200 kgm⁻² day⁻¹ μm, from 100to 200 kgm⁻² day⁻¹ μm or from 75 to 150 kgm⁻² day⁻¹ μm. The polymerizedRTIL monomer may be supported or unsupported.

D. Properties and Uses of Films and Membranes Comprising RTILCompositions

Membranes and films comprising RTILs present a number of uniqueopportunities for the processing and tailoring of polymer materials forapplications including ion conduction polymers, antistatic materials,catalysis, gas separations and water vapor-permeable materials. Perhapsmost importantly, RTILs synthesized as monomers and polymerized in thepresence of non-polymerizable RTILs provide composite materials withenhanced properties. These features allow for the formation ofpoly(RTIL)-RTIL composite gas separation membranes, exhibiting hybridproperties of both RTILs and polymers. For example, incorporation ofjust 20 mol % free RTIL in the cationic polymer membrane yields a stablecomposite material with a CO₂ permeability increase of approximately400% with a 33% improvement to CO₂/N₂ selectivity relative to theanalogous poly(RTIL) membrane lacking any unbound RTIL cations. Thecomposite membranes also show a significant improvement in CO₂/CH₄separation compared to other poly(RTILs) when analyzed via “RobesonPlots.” This new approach to polymer gas separation membranes provides apowerful method to improve the performance of current materials withoutintensive organic synthesis.

For gas separation applications, important parameters are thepermeability (the degree to which the membrane admits a flow of aparticular gas through the membrane) and the separation selectivityprovided by the membrane. For the selectivity of components i over j,S_(i/j) is the permeability of component i divided by the permeabilityof component j. The ideal selectivity is the ratio of the permeabilitysobtained from single gas permeation experiments. The actual selectivity(also called separation selectivity) for a gas mixture may differ fromthe ideal selectivity. For two gas components i and j, a separationselectivity S_(i/j) greater than one implies that the membrane isselectively permeable to component i. If a feedstream containing bothcomponents is applied to one side of the membrane, the permeate streamexiting the other side of the membrane will be enriched in component iand depleted in component j. The greater the separation selectivity, thegreater enrichment of the permeate stream in component i.

In one embodiment, the membranes of the present invention have a carbondioxide/methane (CO₂/CH₄) separation selectivity of 20 or greater, 32 orgreater; 37 or greater, or 40 or greater. In other embodiments, themembranes have a carbon dioxide/methane (CO₂/CH₄) separation selectivityof 17-50, 24-40, or 27-38.

In one embodiment, the membranes of the present invention have a carbondioxide/nitrogen (CO₂/N₂) separation selectivity of 20 or greater, 32 orgreater, 40 or greater, or 44 or greater. In other embodiments, themembranes have a carbon dioxide/nitrogen (CO₂/N₂) separation selectivityof 19-44, 36-41, 22-41, and 22-33.

In one embodiment, the membranes of the present invention have a CO₂permeability of 4 to 108 barrers. In a further embodiment, the membraneshave a CO₂ permeability of 4 to 60 barrers, 9 to 44 barrers, 16 to 44barrers, or 16 to 22 barrers. In other embodiments, the membranes have aCO₂ permeability of 9 barrers or greater, 16 barrers or greater; 40barrers or greater. In a further embodiment, the membranes have a CO₂permeability of 16 or greater, a carbon dioxide/methane (CO₂/CH₄)separation selectivity of 28 or greater, and a carbon dioxide/nitrogen(CO₂/N₂) separation selectivity of 17 or greater. In a furtherembodiment, the membranes have a CO₂ permeability of 22 or greater, acarbon dioxide/methane (CO₂/CH₄) separation selectivity of 32 orgreater, and a carbon dioxide/nitrogen (CO₂/N₂) separation selectivityof 32 or greater.

In another embodiment, the present invention provides a method forseparating a first gas component from a gas mixture containing at leasta first and a second gas component, the method comprising the steps of:a) providing a membrane or film comprising a polymerizedRTIL-unpolymerized RTIL composition as described above; the membrane orfilm having a feed side and a permeate side and being selectivelypermeable to the first gas component over the second gas component; b)applying a feed stream including the first and the second gas componentsto the feed side of the membrane; and c) providing a driving forcesufficient for permeation of the first gas component through themembrane, thereby producing a permeate stream enriched in the first gascomponent from the permeate side of the membrane. Preferably the firstgas component is carbon dioxide (CO₂) and the second gas component ismethane (CH₄) or nitrogen (N₂).

In another embodiment, the composite materials of the present inventionare utilized as catalysts. It has been pointed out that in manysynthetic processes using transition metal catalysts, metalnanoparticles play an important role as the actual catalyst or as acatalyst reservoir. It also has been shown that ionic liquids (ILs),including RTILs, are an appealing medium for the formation andstabilization of catalytically active transition metal nanoparticles.More importantly, ILs can be made that incorporate coordinating groups,for example, with nitrile groups on either the cation or anion (CN-IL).In various C—C coupling reactions catalyzed by palladium catalyst, ithas been found the palladium nanoparticles are better stabilized inCN-IL compared to non-functionalized ionic liquids; thus enhancedcatalytic activity and recyclability are realized.

In another embodiment, the present invention provides membranes andfilms having antistatic properties or static dissipative properties.Typically antistatic materials are considered to have a surfaceresistivity between approximately 10⁹ and 10¹⁴ ohm/cm², while staticdissipative materials have a surface resistivity between approximately10⁶ and 10⁹ ohm/cm². Below a surface resistivity of 10⁹ ohm/cm², chargedissipation can become uncontrolled and allow flammable sources toignite or physically damage electronic circuits and components. In someinstances, however, this type of charge dissipation may be desired, forexample, if the component is electrically grounded or if low resistancemethods to dissipate building charges are required. Accordingly, it isdesirable to provide materials having a wide range of antistatic andcharge dissipative properties.

The polymerized RTIL antistatic materials of the present invention canbe formed using readily available imidazole materials, linkers, tailsand polymerizable groups, and thus are relatively inexpensive toproduce. Additionally, the polymerized RTIL antistatic materials can beproduced using simple chemistry and environmentally friendlier startingmaterials than current antistatic additives. The antistatic behavior canbe maximized through phase formation, and the compatibility of thepolymerized RTIL and poly(RTIL)-RTIL materials can also be adjusted bychanging the bridging linker between the RTIL monomers in the polymer.For example, the counterions utilized with the present antistaticmaterials are easily changed allowing the antistatic material to bemodified according to use with specific host polymers or substrates. Inone embodiment, the index of refraction of the antistatic materials canbe provided to be similar to the host polymer or substrate allowing theoptical-contact clarity and opacity to be fine tuned. The polymerizedRTIL antistatic materials can create a leaching form as dimer, trimer,or oligomeric forms for liquid injections markets but have little to noleaching in the polymeric form. Accordingly, the polymerized RTILantistatic materials can acquire FDA Food Contact/USP VI certificationsby selecting the right anion and non-leaching characteristics as well asutilizing imidazolium as the base building block.

The poly(RTIL) and poly(RTIL)-RTIL materials have similar properties toionomers currently used as antistatic agents, including surfaceresistivity greater than 10⁹ Ohms/cm². Additionally, the polymerizedRTIL antistatic materials provide good heat sealing characteristicssimilar to ionomers. However, the materials of the present invention arenon-metallic and can provide a higher loading of the antistaticcomponent relative to currently used ionomers (approximately a maximumof 20%). Additionally, the antistatic materials of the present inventionhave much higher thermal stability than most low molecular weightadditives, allowing for use in applications such as injection moldingpolycarbonates at temperatures greater than 200° C. The polymerized RTILantistatic materials are also less likely to react to blowing agents toproduce urethane and olefin foam products like currently used antistaticadditives. In embodiments utilizing imidazolium as the polymerized andnon-polymerized RTIL cation, the material should prove to be much lesscorrosive than current antistatic additives.

In one embodiment, the present invention provides a membrane or filmcomprising a polymerized RTIL-unpolymerized RTIL composition asdescribed above where the membrane or film has a surface resistivity of1.0×10⁹ ohm/cm² or greater, or 4.0×10⁹ ohm/cm² or greater at a 10 or 100volt potential. In a further embodiment, the membrane or film has asurface resistivity of 4.9×10⁹ ohm/cm² or greater at a 10 voltpotential, and/or a surface resistivity of 4.2×10⁹ ohm/cm² or greater ata 100 volt potential.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the gas permeabilities and selectivities for three RTILpolymers. Polymer 1 and Polymer 2 are the same except for the anion (BR⁻and Tf₂N⁻, respectively). Polymer 3 is the same as Polymer 2 except thatPolymer 3 further comprises 20 mol % of a non-polymerized RTIL (hmim).

FIG. 2 shows a “Robeson Plot” for CO₂/CH₄ separations using thepoly(RTIL) and poly(RTIL)-RTIL materials of FIG. 1.

FIG. 3 shows a “Robeson Plot” for CO₂/N₂ separations using thepoly(RTIL) and poly(RTIL)-RTIL materials of FIG. 1.

FIG. 4 shows a “Robeson Plot” for H₂/CO₂ separations with Polymer 1 fromFIG. 1.

FIG. 5 shows a representation of a poly(RTIL)-RTIL composite material ofthe present invention containing two opposing layers of polymer boundimidazolium cations (+), [Tf₂N] anions (−), and free [C₂mim] cations(also +) between the polymer layers.

FIG. 6 shows RTIL-based monomers used for fabrication of poly(RTIL) andpoly(RTIL)-RTIL gas separation membranes in some embodiments of thepresent invention.

FIG. 7 shows the structure of [C₂mim][Tf₂N], a non-polymerized RTILcation and anion used in some composites of the present invention aswell as a molten RTIL.

FIG. 8 shows a “Robeson Plot” for CO₂/N₂ separations for poly(RTIL)membranes and poly(RTIL)-[C₂mim][Tf₂] composite membranes.

FIG. 9 shows a “Robeson Plot” for CO₂/CH₄ separations for poly(RTIL)membranes and poly(RTIL)-[C₂mim][Tf₂] composite membranes.

FIG. 10 shows the general structure of a styrene-containing,imidazolium-based RTIL monomer used to make poly(RTIL)-RTIL compositemembranes.

FIG. 11 shows exemplary components of a poly(RTIL)-RTIL compositemembrane using monomer 1a from FIG. 10 and [C₂mim][Tf₂].

FIG. 12 shows structures of monomer 1d from FIG. 10 and [C₂mim][X-]salts used to fabricate exemplary poly(RTIL)-RTIL composite gasseparation membranes.

FIG. 13a shows a “Robeson plot” for CO₂/N₂ annotated to includepoly(RTIL)-RTIL composite membranes of FIG. 12. FIG. 13b shows a“Robeson plot” for CO₂/CH₄ annotated to include poly(RTIL)-RTILcomposite membranes of FIG. 12.

FIG. 14: Structures of RTILs and RTIL monomers and polymers.

FIG. 15: Structures of diol RTILs and their bulk interactions withwater.

FIG. 16: Structure of a diol-RTIL monomer and the poly(diol-RTILpolymer).

FIG. 17: Representative water vapor transport test plot. Data points arethe average of three independent sample runs performed in the same roundof testing. This data was obtained using the glovebox test method.

DETAILED DESCRIPTION OF THE INVENTION Definitions

As used herein, the term “alkyl” refers to a monoradical of a branchedor unbranched (straight-chain or linear) saturated hydrocarbon and tocycloalkyl groups having one or more rings. Alkyl groups as used hereininclude those having from 1 to 20 carbon atoms, preferably having from 1to 10 carbon atoms. Alkyl groups include small alkyl groups having 1 to3 carbon atoms. Alkyl groups include medium length alkyl groups havingfrom 4-10 carbon atoms. Alkyl groups include long alkyl groups havingmore than 10 carbon atoms, particularly those having 10-20 carbon atoms.Cyclic alkyl groups include those having one or more rings. Cyclic alkylgroups include those having a 3-, 4-, 5-, 6-, 7-, 8-, 9- or 10-membercarbon ring and particularly those having a 3-, 4-, 5-, 6-, or 7-memberring. The carbon rings in cyclic alkyl groups can also carry alkylgroups. Cyclic alkyl groups can include bicyclic and tricyclic alkylgroups. Alkyl groups are optionally substituted. Substituted alkylgroups include among others those which are substituted with arylgroups, which in turn can be optionally substituted. Specific alkylgroups include methyl, ethyl, n-propyl, iso-propyl, cyclopropyl,n-butyl, s-butyl, t-butyl, cyclobutyl, n-pentyl, branched-pentyl,cyclopentyl, n-hexyl, branched hexyl, and cyclohexyl groups, all ofwhich are optionally substituted. Substituted alkyl groups include fullyhalogenated or semihalogenated alkyl groups, such as alkyl groups havingone or more hydrogens replaced with one or more fluorine atoms, chlorineatoms, bromine atoms and/or iodine atoms. Substituted alkyl groupsinclude hydroxyl groups, diol groups, and alkoxy groups. An alkoxy groupis an alkyl group linked to oxygen and can be represented by the formulaR—O. Examples of alkoxy groups include, but are not limited to, methoxy,ethoxy, propoxy, butoxy, and heptoxy. Alkoxy groups include substitutedalkoxy groups wherein the alky portion of the groups is substituted asprovided herein in connection with the description of alkyl groups.

The term “alkenyl” refers to a monoradical of a branched or unbranchedunsaturated hydrocarbon group having one or more double bonds and tocycloalkenyl groups having one or more rings wherein at least one ringcontains a double bond. Alkenyl groups include those having 1, 2 or moredouble bonds and those in which two or more of the double bonds areconjugated double bonds. Alkenyl groups include those having from 1 to20 carbon atoms, preferably having from 1 to 10 carbon atoms. Alkenylgroups include small alkenyl groups having 2 to 3 carbon atoms. Alkenylgroups include medium length alkenyl groups having from 4-10 carbonatoms. Alkenyl groups include long alkenyl groups having more than 10carbon atoms, particularly those having 10-20 carbon atoms. Cyclicalkenyl groups include those having one or more rings. Cyclic alkenylgroups include those in which a double bond is in the ring or in analkenyl group attached to a ring. Cyclic alkenyl groups include thosehaving a 3-, 4-, 5-, 6-, 7-, 8-, 9- or 10-member carbon ring andparticularly those having a 3-, 4-, 5-, 6- or 7-member ring. The carbonrings in cyclic alkenyl groups can also carry alkyl groups. Cyclicalkenyl groups can include bicyclic and tricyclic alkyl groups. Alkenylgroups are optionally substituted. Substituted alkenyl groups includeamong others those which are substituted with alkyl or aryl groups,which groups in turn can be optionally substituted. Specific alkenylgroups include ethenyl, prop-1-enyl, prop-2-enyl, cycloprop-1-enyl,but-1-enyl, but-2-enyl, cyclobut-1-enyl, cyclobut-2-enyl, pent-1-enyl,pent-2-enyl, branched pentenyl, cyclopent-1-enyl, hex-1-enyl, branchedhexenyl, cyclohexenyl, all of which are optionally substituted.Substituted alkenyl groups include fully halogenated or semihalogenatedalkenyl groups, such as alkenyl groups having one or more hydrogensreplaced with one or more fluorine atoms, chlorine atoms, bromine atomsand/or iodine atoms.

The term “alkynyl” refers to a monoradical of an unsaturated hydrocarbonhaving one or more triple bonds (C≡C) and to cycloalkynyl groups havingone or more rings wherein at least one ring contains a triple bond.Alkynyl groups include those having from 2 to 20 carbon atoms,preferably having from 2 to 10 carbon atoms. Alkynyl groups includesmall alkynyl groups having 2 to 3 carbon atoms. Alkynyl groups includemedium length alkynyl groups having from 4-10 carbon atoms. Alkynylgroups include long alkynyl groups having more than 10 carbon atoms,particularly those having 10-20 carbon atoms. The term “cycloalkynyl”refers to cyclic alkynyl groups of from 3 to 20 carbon atoms having asingle cyclic ring or multiple condensed rings in which at least onering contains a triple bond (C≡C). Descriptions herein with respect toalkynyl groups apply generally to cycloalkynyl groups. Alkynyl groupsare optionally substituted. Substituted alkynyl groups include amongothers those which are substituted with alkyl, alkenyl or aryl groups,which groups in turn can be optionally substituted. Substituted alkynylgroups include fully halogenated or semi-halogenated alkynyl groups,such as alkynyl groups having one or more hydrogens replaced with one ormore fluorine atoms, chlorine atoms, bromine atoms and/or iodine atoms.

The term “aryl” refers to a chemical group having one or more 5-, 6- or7-member aromatic or heterocyclic aromatic rings. An aromatichydrocarbon is a hydrocarbon with a conjugated cyclic molecularstructure. Aryl groups include those having from 6 to 20 carbon atoms.Aryl groups can contain a single ring (e.g., phenyl), one or more rings(e.g., biphenyl) or multiple condensed (fused) rings, wherein at leastone ring is aromatic (e.g., naphthyl, dihydrophenanthrenyl, fluorenyl,or anthryl). Heterocyclic aromatic rings can include one or more N, O,or S atoms in the ring. Heterocyclic aromatic rings can include thosewith one, two or three N, those with one or two O, and those with one ortwo S, or combinations of one or two or three N, O or S. Aryl groups areoptionally substituted. Substituted aryl groups include among othersthose which are substituted with alkyl or alkenyl groups, which groupsin turn can be optionally substituted. Specific aryl groups includephenyl groups, biphenyl groups, pyridinyl groups, and naphthyl groups,all of which are optionally substituted. Substituted aryl groups includefully halogenated or semihalogenated aryl groups, such as aryl groupshaving one or more hydrogens replaced with one or more fluorine atoms,chlorine atoms, bromine atoms and/or iodine atoms.

Optional substituents for alkyl, alkenyl and aryl groups include amongothers:

—COOR where R is a hydrogen or an alkyl group or an aryl group and morespecifically where R is methyl, ethyl, propyl, butyl, or phenyl groupsall of which are optionally substituted;

—COR where R is a hydrogen, or an alkyl group or an aryl groups and morewhere R is methyl, ethyl, propyl, butyl, or phenyl groups all of whichgroups are optionally substituted;

—CR(OH)₂ where R is a branched alkyl group;

—CON(R)₂ where each R, independently of each other R, is a hydrogen oran alkyl group or an aryl group and more specifically where R is methyl,ethyl, propyl, butyl, or phenyl groups all of which groups areoptionally substituted; R and R can form a ring which may contain one ormore double bonds;

—OCON(R)₂ where each R, independently of each other R, is a hydrogen oran alkyl group or an aryl group and more specifically where R is methyl,ethyl, propyl, butyl, or phenyl groups all of which groups areoptionally substituted; R and R can form a ring which may contain one ormore double bonds;

—N(R)₂ where each R, independently of each other R, is an alkyl group,acyl group or an aryl group and more specifically where R is methyl,ethyl, propyl, butyl, or phenyl or acetyl groups all of which areoptionally substituted; or R and R can form a ring which may contain oneor more double bonds.

—SR, —SO₂R, or —SOR where R is an alkyl group or an aryl groups and morespecifically where R is methyl, ethyl, propyl, butyl, phenyl groups allof which are optionally substituted; for —SR, R can be hydrogen;

—OCOOR where R is an alkyl group or an aryl groups;

—SO₂N(R)₂ where R is a hydrogen, an alkyl group, or an aryl group and Rand R can form a ring.

As used herein, the term “alkylene” refers to a divalent radical derivedfrom an alkyl group or as defined herein. Alkylene groups in someembodiments function as attaching and/or spacer groups in the presentcompositions. Compounds of the present invention include substituted andunsubstituted C₁-C₂₀ alkylene, C₁-C₁₀ alkylene and C₁-C₄ alkylenegroups. The term “alkylene” includes cycloalkylene and non-cyclicalkylene groups. As used herein, the term “cycloalkylene” refers to adivalent radical derived from a cycloalkyl group as defined herein.

As used herein, the term “alkenylene” refers to a divalent radicalderived from an alkenyl group as defined herein. Alkenylene groups insome embodiments function as attaching and/or spacer groups in thepresent compositions. Compounds of the present invention includesubstituted and unsubstituted C₁-C₂₀ alkenylene, C₁-C₁₀ alkenylene andC₁-C₅ alkenylene groups. The term “alkenylene” includes cycloalkenyleneand non-cyclic alkenylene groups. As used herein, the term“cylcoalkenylene” refers to a divalent radical derived from acylcoalkenyl group as defined herein. Cycloalkenylene groups in someembodiments function as attaching and/or spacer groups in the presentcompositions.

As used herein, the term “alkynylene” refers to a divalent radicalderived from an alkynyl group as defined herein. Alkynylene groups insome embodiments function as attaching and/or spacer groups in thepresent compositions. Compounds of the present invention includesubstituted and unsubstituted C₂-C₂₀ alkynylene, C₂-C₁₀ alkynylene andC₂-C₅ alkynylene groups. The term “alkynylene” includes cycloalkynyleneand non-cyclic alkynylene groups.

As used herein, the term “arylene” refers to a divalent radical derivedfrom an aryl group as defined herein. Arynylene groups in someembodiments function as attaching and/or spacer groups in the presentcompositions. Compounds of the present invention include substituted andunsubstituted C₂-C₂₀ arylene, C₂-C₁₀ arylene and C₂-C₅ arylene groups.

As used herein, a “polymerized RTIL” refers to a polymer comprisingmultiple repeating units having RTIL cations and any associated anions.The polymerized RTIL can be formed by polymerizing RTIL monomers whichhave one or more polymerizable groups which allow covalent bonding ofthe monomer to another molecule such as another monomer, polymer orcross-linking agent. Suitable polymerizable groups include acrylate,methacrylate, diene, vinyl, (halovinyl), styrenes, vinylether, hydroxygroups, epoxy or other oxiranes (halooxirane), dienoyls, diacetylenes,styrenes, terminal olefins, isocyanides, acrylamides, and cinamoylgroups. The RTIL polymer may also comprise an initiator and/or across-linking agent.

Polymerized RTILs, Gas Permeability and Selectivity

Polymerized RTILs, also referred to herein as “poly(RTILs)”, have beenstudied as neat materials for ion conduction, gas sorption, and gasseparation membranes. These polymers have largely consisted ofpoly(acrylate) or poly(styrene) backbones with imidazolium or ammoniumcations tethered as side chains. (Ohno, Macromol. Symp. 2007; 249/250:551-556; Nakajima et al., Polymer 2005; 46: 11499-11504; Yoshio et al.,Mol. Cryst. Liq. Cryst. 2004; 413: 2235-2244). In this configuration,the anion is not chemically bonded to the main polymer chain. Polyanionssuch as poly(styrene sulfonic acid salts) have also been employed, alongwith poly-(zwitterions) and copolymers. The most successful supportmatrices to incorporate RTILs within a solid material have featuredpolymer-bound, immobilized imidazolium cations and/or hydrogen bonddonors such as primary alcohols. The present invention provides a numberof RTIL polymers that are capable of interfacing with non-polymerizedRTILs that remain unbound from the polymer. Additionally, active agents,such as metal complexes, acids or bases, can be added with thenon-polymerized RTIL, creating an active material. Uses of thesepoly(RTIL)-RTIL composites may include antistatic materials, gasseparation membranes, and gels.

The effects of structure on permeability and CO₂/N₂ and CO₂/CH₄separation performance in solid, poly(RTIL) gas separation membranes hasbeen studied using a variety of functionalized RTIL monomers containingalkyl, oligo(ethylene) glycol, and nitrile-terminated alkyl groups, aswell as self-crosslinking “gemini” RTIL (GRTIL) monomers (Bara et al.,Ind. Eng. Chem. Res. 2007; 46: 5397-5404; Bara et al., J. Memb. Sci.2008; 316: 186-191; Bara et al., J. Memb. Sci. 2007;doi:10.1016/j.memsci.2007.12.033). A representation of the various RTILmonomers used to form poly(RTIL) membranes of the present invention isshown in FIGS. 1,6 and 10.

FIG. 1 shows the gas permeabilities and selectivities for three RTILpolymers. The RTIL monomer is the same for each polymer:

However, the associated anion is different between Polymer 1 and Polymer2 (Br⁻ and Tf₂N⁻, respectively). Polymer 3 uses the same anion (Tf₂N⁻)as Polymer 2 but further comprises 20 mol % of a non-polymerized RTIL(hmim):

The results in FIG. 1 indicate that changing the anion of the compositecan be used to adjust the gas permeability and selectivity.Additionally, the presence of the non-polymerized RTIL can be used toenhance the gas permeability and/or the gas pair selectivity.

“Robeson Plots” are widely used for gauging the progress of polymer gasseparation membranes (Robeson L M, J. Memb. Sci. 1991; 62:165-185).These log-log charts plot ideal permselectivity for a gas pair againstthe ideal permeability of the more permeable gas. The “upper bound” canbe viewed as a target for researchers to exceed in the development ofnew membranes. The further to the upper right a material lies is oneindicator of its potential for industrial implementation (Baker, R W,Ind. Eng. Chem. Res. 2002; 41: 1393-1411). The “upper bound” hastraditionally been defined by glassy polymers with large diffusionselectivities (Robeson L M, J. Membr. Sci. 1991; 62:165-185; Freeman BD., Macromolecules 1999; 32: 375-380). In recent years, many polymers,especially those composed of polymers with polar linkages, such aspoly(ethylene glycol) (PEG) derivatives have exceeded the “upper bound”as they exhibit large solubility selectivities, while allowing for therapid permeation of each gas. Gas permeability and permselectivity datafor these poly(RTIL) membranes, including poly(RTIL)-RTIL membranes, areshown in FIGS. 2-4.

Poly(RTILs) can be formed as powders but are also able to be formed asthin films, allowing for the these materials to be used as gasseparation membranes or in other thin film applications. For example,poly(RTILs) are an attractive alternative platform to SILMs, as thechemistry of RTILs can be utilized for selective CO₂ transport, whilesignificantly improving the mechanical stability of the membrane. Suchmembranes are structurally stable and can further be generated to beoptically transparent.

Significant changes in gas permeability and gas pair selectivity canoccur with small changes to the structure of the cationic polymerprimarily through modification of the imidazolium cation in its parentmonomer. The most permeable membranes typically have been those withlonger side chains on the imidazolium cation, and the most selectivematerials typically have been those with polar, oligo(ethylene glycol)appendages. Analogous poly(RTIL) monomers (FIG. 6) with styrene oracrylate (not shown) backbones exhibited very similar properties.Examples of RTILs and polymerizable RTILs with two joined (i.e., gemini)imidazolium headgroups has been reported in the literature (Anderson etal., J. Am. Chem. Soc. 2005, 127: 593-604; Jin et al., J. Mater. Chem.2006, 16:1529-1535; Nakajima et al., Polymer 2005, 46:11499-11504).“Gemini” or poly(GRTILs) were not found to have high permeability orselectivity, as they are highly crosslinked and restrict the movement ofall gases.

While tailoring the imidazolium based monomers to improve gasselectivity in the poly(RTIL) membrane has been successful, thepermeabilities of poly(RTIL) membranes fall far short of their molten,RTIL counterparts. Table 1 illustrates the vast differences in CO₂permeability between a series of poly(RTIL) membranes and a widely usednon-polymerized RTIL, 1-ethyl-3-methylimidazolium andbis(trifluoromethane)sulfonimide, [C₂mim][Tf₂N] (shown in FIG. 7). Theideal separation factors are taken to be the ratio of the idealpermeability of CO₂ to that of the other gas of interest.

TABLE 1 CO₂ permeability and CO₂/N₂ and CO₂/CH₄ selectivities indifferent classes of poly(RTIL) membranes and a widely studied RTIL(C₂mim). Poly(1-4) refer to the polymers disclosed in Figure 6. MembraneCO₂ permeability^(a) CO₂/N₂ CO₂/CH₄ Poly(1a-c): C_(n)CH₃  9-32 28-3217-39 Poly(2): Gemini 4 22-28 27-32 Poly(3a, b)OEG_(p) 16-22 41-44 29-33Poly(4): C_(n)CN 4-8 37-40 30-37 [C₂min][Tf₂N] 1000 21 11 ^(a)CO₂permeability in barrers. 1 barrer = 10 ⁻¹⁰ cm³ (STP)cm/cm² s cm Hg.

The major factor retarding the rate gases transport through poly(RTIL)membranes relative to those observed in SILMs has been a large decreasein gas diffusion through the solid material. For example, the diffusioncoefficient for CO₂ in [C₂mim][Tf₂N] at 303K has been measured as 8×10⁻⁶cm²/s, and experiments with poly(RTILs) show that diffusion coefficientsfor CO₂ can range from approximately 1×10⁻⁹ to 1×10⁻⁷ cm₂/s in thepolymer membranes. Polymerizing RTILs causes a very large decrease ingas diffusion and, in turn, permeability of ca. 2-3 orders of magnitude.While gas diffusion through a dense, solid film is expected to beseveral orders of magnitude less than that through a dense liquid film,it is believed development into improving gas diffusion (whilemaintaining mechanical integrity) in poly(RTIL) membranes is the nextstep toward making them a competitive gas separation technology. Theincorporation of a “free” RTIL component into the poly(RTIL) matrix hasbeen shown to be successful in improving ion conductivity in poly(RTIL)films, and appears to be an interesting approach to improve gaspermeability through similar materials.

To this end, a poly(RTIL)-RTIL composite membrane is fabricated throughthe photopolymerization of a simple imidazolium-based RTIL monomer (suchas shown as polymer 1a in FIG. 6) in the presence of [C₂mim][Tf₂N](structures shown in FIG. 7). Monomer 1a of FIG. 6 was chosen as itrepresents perhaps the simplest possible photopolymerizable RTILmonomer. [C₂mim][Tf₂N] was selected as it is a widely studied RTIL, andis miscible with the monomers of FIG. 6.

While a large number of poly(RTIL)-RTIL combinations are possible, thesesimple, readily synthesized components can provide great insight intohow poly(RTIL)-RTIL composites might function on a basic level, beforemore complex systems are designed to optimize performance. The compositestudied in this work contains 80 mol % imidazolium cations bound to thepolystyrene chain with 20 mol % of the imidazolium cations remaining as“free” within the material along with “free” anions, and is generallyillustrated in FIG. 5.

The neat poly(RTIL) formed from the monomers of FIG. 6 exhibited a CO₂permeability of nine barrers with ideal separation factors for CO₂/N₂=32and CO₂/CH₄=38. The composite material with 20 mol % free cations showedan ideal CO₂ permeability of 44 barrers with ideal separation factors ofCO₂/N₂=40 and CO₂/CH₄=28. Through the use of a poly(RTIL)-RTIL compositemembrane for gas separations, CO₂ permeability increased byapproximately 400% and CO₂/N₂ selectivity increased by approximately 25%relative to the neat poly(RTIL), and the membrane exceeds the “upperbound” of a “Robeson Plot” for this separation. While CO₂/CH₄ separationdid decrease by approximately 33%, the gains in CO₂ permeability stillrepresent progress for this separation through poly(RTIL)-basedmembranes, as the performance moved closer to the “upper bound” of a“Robeson Plot” for CO₂/CH₄, relative to the neat poly(RTIL). Theseinitial performance data illustrate that poly(RTILs) may be an idealsupport matrix for stabilizing RTILs within polymer gas separationmembranes, with the composite membranes exhibiting highly improvedperformance in CO₂-based separations.

One of the most attractive features of imidazolium-based RTILs is theirability to be chemically tailored to improve performance in particularapplications. The influences of various functional groups on theinteractions of RTILs with CO₂ and other gases have been previouslyexplored. Early work focused on the effect of alkyl chain length and/oranion in imidazolium-based RTILs. However, given the range of functionalgroups known to impact gas solubility in molecular solvents (i.e.,CH₃CN, MeOH, acetone, etc.), it became apparent that the study of RTILsfor gas separations should not be limited to strictlyalkyl-functionalized systems. The incorporation of polar functionalgroups such as oligo(ethylene glycol) units and nitrile-terminated alkylchains has been reported to increase CO₂/N₂ and CO₂/CH₄ solubilityselectivity in RTILs, with little detriment to CO₂ solubility. RTILscontaining fluoroalkyl groups have also been shown to provide modestimprovements in CO₂ solubility relative to their alkyl-functionalizedanalogues. When tested in an SILM configuration,fluoroalkyl-functionalized RTILs displayed improved CO₂/CH₄ selectivityrelative to alkyl-functionalized RTILs but diminished CO₂/N₂selectivity. Also, an imidazolium-based RTIL featuring a primary aminetethered to the cation has been shown to be capable of reversible CO₂capture.

RTIL monomers can be synthesized to contain a variety of chemical groups(R groups in FIG. 10) in addition to the polymerizable unit.Imidazolium-based monomers containing n-alkyl chains (polymers 1a-c inFIG. 10), short oligo(ethylene glycol) linkages (polymers 1d and 1e inFIG. 10), and nitrile-terminated n-alkyl chains (polymers if and 1g inFIG. 10) have been successfully synthesized. “Gemini” or difunctionalRTIL monomers are also possible. Monomers that were previouslysynthesized featured bis-(trifluoromethane)sulfonimide (Tf₂N) anions.The chemical nature of the polymerizable RTIL monomer has significanteffects on the gas separation performance of the resultant poly(RTIL)gas separation membrane. Increasing the length of the nonpolymerizablesubstituent (R groups in FIG. 10) results in increased permeability forall gases. For n-alkyl chains, increasing the length of the substituentresulted in decreased ideal selectivity in CO₂/N₂ and CO₂/CH₄separations.

The ideal permeability of CO₂ in poly(RTIL) membranes witholigo(ethylene glycol) substituents was similar to that observed inpoly(RTILs) containing n-alkyl substituents. However, with increasinglength of oligo(ethylene glycol) substituent, the ideal selectivity ofCO₂/N₂ was observed to increase, while CO₂/CH₂ decreased. A similartrend in ideal selectivity behavior was observed in poly(RTIL) membranescontaining alkyl-terminated nitrile groups, but those poly(RTIL)membranes suffered from CO₂ permeabilities that were less than theoriginal alkyl-functionalized systems. Permeability in poly(RTIL)membranes ranged from 4 to 39 barrers, with CO₂/N₂ selectivities rangingfrom 28 to 44 and CO₂/CH₄ selectivities of 17-39. Alkyl-functionalizedpoly(RTILs) approximate the “upper bound” of the “Robeson plot” forCO₂/N₂ while those with oligo(ethylene glycol) and nitrile-terminatedalkyl groups exceed an “upper bound” for this separation. None of thepoly(RTIL) membranes have been observed to exceed the “upper bound” forCO₂/CH₄ separation. All types of poly(RTIL) membranes exhibited CO₂permeabilities of only 1-10% of that of the most permeable SILMs,primarily as a result of slower gas diffusion in solids than liquids.

Modification of the substituent on the imidazolium cation in poly(RTILs)is observed to have a much greater effect on the selectivity of themembrane than on the permeability of CO₂. While an understanding of howto improve the CO₂ selectivity of poly(RTILs) through substituentmodification has been achieved, it is also very desirable to improve CO₂permeability through poly(RTIL) membranes to better compete with thehigh permeability of SILMs and high-performance polymer membranes ingeneral. One possible approach is to increase the length of thesubstituent group on the RTIL monomer. This method could increasepermeability at the expense of the diminished concentration of ionswithin the membrane, losing many of the desirable properties of the RTILplatform. The resulting polymers would more resemble the substituent(i.e., PE or PEG) rather than a poly(RTIL). However, the formation ofpoly(RTIL)-RTIL composite membranes is an even more straightforwardapproach to improving CO₂ permeability.

For example, as illustrated in FIG. 11, the RTIL monomer depicted aspolymer 1a in FIG. 10 was polymerized in the presence of 20 mol % of1-ethyl-3-methylimidazolium bis(trifluoromethane)-sulfonimide, alsoreferred to herein as [C₂mim][Tf₂N], a common RTIL (shown in FIG. 7).The resulting solid poly(RTIL)-RTIL composite was homogeneous andexhibited no evidence of phase separation, even after many months ofstorage at ambient conditions. RTILs within poly(RTIL) matrices shouldbe viewed as very different from traditional additives or plasticizersin conventional polymers. Not only are RTILs nonvolatile, they alsoexperience significant ionic interactions with poly(RTILs). It isproposed that the charged backbone of poly(RTILs) strongly holds RTILswithin the matrix and prevents phase separation.

The permeability of CO₂ of a polymer made from monomer 1a of FIG. 6(without non-polymerized RTIL) was first reported to be 9.2 barrers,while the composite of polymer 1a and [C₂mim][Tf₂N] was found to have aCO₂ permeability of 44 barrers, approximately a 400% increase. CH₄ andN₂ exhibited 600% and 300% increases in their respective permeabilities.The increased permeabilities were attributed to more rapid gas diffusionthrough a composite with “free” or mobile ions. As a result, CO₂/N₂selectivity in the composite membrane was found to be greater than thatof the polymer alone, with values 40 and 32, respectively. CO₂/CH₄selectivity experienced a decline in the composite relative to just thepolymer, falling from a value of 39 for just the polymer to 28 in thecomposite. However, an ideal CO₂/CH₄ selectivity of 28 still representsan improvement over many poly(RTIL) membranes.

The nature of the anion associated with the “free” RTIL component has adramatic effect on gas permeability. A poly(RTIL)-RTIL compositemembrane containing exclusively Tf₂N anions was observed to have anideal CO₂ permeability of 60 barrers. Poly(RTIL)-RTIL compositemembranes containing mixed anion systems with OTf, dca, or SbF₆ were allfound to have very similar ideal CO₂ permeabilities of ca. 40 barrers.The nature of the anion was found to have a very subtle effect on idealpermeability selectivity for CO₂/N₂ and CO₂/CH₄ separations, whichranged from 36 to 39 and 24 to 27, respectively. The compositecontaining only Tf₂N anions defined the lower limit of ideal selectivityin both separations. Plotting the performance of these poly(RTIL)-RTILcomposites on “Robeson plots” reveals that CO₂/N₂ separations exceed the“upper bound” of the chart and that these poly(RTIL)-RTIL compositesrepresent a significant improvement to previous poly(RTIL) membranes(see FIG. 13a ). When the same is done for a similar chart of CO₂/CH₄performance, poly(RTIL)-RTIL composites are also shown as an improvementupon previous poly(RTIL) membranes (see FIG. 13b ). Whilepoly(RTIL)-RTIL membranes are also below the “upper bound” of this“Robeson plot”, they are closer to that line than previous poly(RTIL)membranes.

Tf₂N anions have been typically used in the poly-(RTIL) membranes as theparent RTIL monomers with those anions are most convenient tosynthesize. However, RTILs with a wide variety of anions are readilysynthesized or are commercially available. While the effect ofsubstituent groups on poly(RTIL) gas separation membranes have alreadyexplored, how those substituents will interact with “free” RTILs in thecomposite materials is not always clear. Thus, the effect of the type ofanion in the “free” RTIL, as well as the structure of the cation, canvary and is of interest. Additionally, the concentration of “free” RTILin the composite may have the most dramatic effect on performance, asthe permeability differences between poly(RTILs) and RTILs span a rangeof nearly 3 orders of magnitude.

EXAMPLES Example 1 Membrane Fabrication

[C₂mim][Tf₂N] (0.614 g, 1.57 mmol) was added to monomer 1a of FIG. 6(3.00 g, 6.26 mmol) and the 1:4 (mol:mol) mixture was homogenized to asingle liquid phase on a vibrating mixer. Divinylbenzene (0.034 g, 0.33mmol) was added and the mixing step repeated. Finally,2-hydroxy-2-methylpropiophenone (0.030 g, 0.18 mmol) was added to thesolution and the mixing step repeated a final time. The solution wascast onto a 50×50 cm² piece of a porous polymer support (Supor200, Pall,Ann Arbor, Mich., USA) on top of a quartz plate. A second, identicalquartz plate was placed on top and pressure was applied manually tospread the monomer evenly through the support. The excess monomerremained between the quartz plates. The plates were then placed under a365 nm UV light for 30 min. After this time, the plates were separatedwith a clean razor blade and the supported polymer film peeled from thesurface. The supported area was then punched with a 47 mm diameterstainless steel die. The mass of the membrane and support was found tobe 0.574 g. The mass of a 47 mm diameter section of the support has beenfound to be 0.070 g on average. Thus, the amount of poly(RTIL)-RTILcomposite on the support was 0.504 g. The density of the composite wasdetermined to be 1.42 g/cm³. The thickness of the membrane was found tobe approximately 200 μm.

[C₂mim][Tf₂N] and monomer 1a of FIG. 6 were synthesized according topreviously published methods (Bara et al., Ind. Eng. Chem. Res. 2007;46: 5397-5404; Finotello et al., Ind. Eng. Chem. Res. 2008; 47:3453-3459). All other chemicals were used as received from Sigma-Alrdich(Milwaukee, Wis., USA). All gases were purchased from AirGas (Radnor,Pa., USA) and were of at least 99.99% purity.

Example 2 Gas Permeability Experiments

Ideal (single) single gas permeability experiments of the polymers ofExample 1 with CO₂, N₂, and CH₄ were carried out at 295K using atime-lag apparatus. Details on the construction, operation, andcalculations associated with this equipment can be found as published byour group (Bara et al., Ind. Eng. Chem. Res. 2007; 46: 5397-5404; Baraet al., J. Memb. Sci. 2007; 288:13-19). The membrane was degassed underdynamic vacuum of <1 torr for at least 16 hr between experiments. Adriving force of ca. 2 atm was applied against initial vacuumdownstream. Automated data collection was performed using LabView(National Instruments, Austin, Tex., USA). The ideal permeability forCO₂, N₂, and CH₄ along with the ideal permselectivities of CO₂/N₂ andCO₂/CH₄ are presented in Table 2.

TABLE 2 Ideal gas permeabilities and permselectivities in the compositemembrane and the neat polymer Poly(RTIL) Permeability (barrers)Permselectivity membrane CO₂ N₂ CH₄ CO₂/N₂ CO₂/CH₄ Poly(1a) 9.2 ± 05 0.29 ± 0.01 0.24 ± 0.01 32 39 Poly(1a) + 44 ± 3  1.1 ± 0.1 1.6 ± 0.1 3927 20 mol % [C₂mim][Tf₂N]

Assuming solution-diffusion is the mode of transport through poly(RTILs)and poly(RTIL)-RTIL composite membranes, the permeability of a singlegas (Pi) can be broken down as the product of its solubility (Si) anddiffusivity (Di) through the material (equation 1, Wijmans et al., J.Memb. Sci. 1995; 107: 1-21):

Pi=Si·Di

The ideal permeselectivity (α_(i,j)) is taken as the ratio of thepermeability of the more permeable gas (i) to that of the less permeablespecies (j). The permselectivity can be broken down into S and Dcontributions (equation 2):

$a_{i,j} = {\frac{Pi}{Pj} = {\frac{Si}{Sj} \cdot \frac{Di}{Dj}}}$

As can be seen from the table, the permeability of all gases increaseddramatically in the poly(RTIL)-RTIL composite membrane, indicating thatthe addition of only 20 mol % free [C₂mim][Tf₂N] into the polymer canhave large effects on gas permeability. The permeability increases forCO₂, N₂, and CH₄ were roughly 400%, 300%, and 600%, respectively. Theobserved permeability of CO₂ in the composite membrane is beyond whathas been observed in any of the poly(RTIL) membranes thus far.

Increased gas permeability may be attributed to the presence of thenon-polymerizable component, [C₂mim][Tf₂N]. The free ion pairs serve tocreate and fill volume between the polymer chains, increasing thediffusivity, and in turn, permeability of each gas through the membrane.Furthermore, as [C₂mim][Tf₂N] does not have any covalent bonds to thepolymer backbone, it may exhibit some mobility through the membrane.These free ions should further increase gas diffusion, as would beexpected from a liquid component encapsulated in a polymer film.However, [C₂mim][Tf₂N], and other RTILs, cannot be viewed as atraditional liquid phase additive or plasticizer when inside apoly(RTIL) matrix. The RTIL component is non-volatile and cannot escapethe membrane when subjected to vacuum or sweep gas. As salts, RTILsshould also undergo significant non-covalent interactions with thecharges associated with the polymer backbone, and at low concentrationsare not expected to be leached from polymer in any appreciable manner byforces such as the pressure differential across the membrane. After theabove experiments were completed, no residual liquid RTIL was foundpresent inside the membrane apparatus, and the mass of the membrane wasthe same as it was before gas permeability testing began. Furthermore,no phase separation was observed after storing the membrane underambient conditions for several months. These observations indicate thatthese composites are stable to at least 20 mol % of RTIL. While thepermeability values for the composite membrane are still much lower thanthe permeability of neat [C₂mim][Tf₂N] this new composite materialrepresents a simple method to improve CO₂ permeability throughpoly(RTIL)-based membranes without sacrificing the CO₂/N₂ selectivity.

In fact, ideal CO₂/N₂ permselectivity actually exhibits a slightincrease when [C₂mim][Tf₂N] is incorporated in the polymer structure.Initial work with the neat polymer found that the diffusion of N₂ wasfaster than CO₂ through the poly(RTIL) membrane, and separationselectivity was favored by large solubility differences between the twogases. In bulk liquid RTILs, it is expected that there is little or nodifference in diffusion rates among CO₂, N₂, and CH₄, and separation isachieved solely through CO₂ solubility being much higher than that ofN₂, and to a lesser extent CH₄. In the case of a poly(RTIL)-RTILcomposite membrane, the restriction of CO₂ diffusion may be eased, andthe diffusion of CO₂ now is less of an impediment to the separation ofCO₂/N₂. In contrast, CO₂/CH₄ permselectivity decreased by ca. 25%. Inthe neat polymer, there were favorable differences in both solubilityand selectivity for CO₂ separation from CH₄. The neat polymer monomer 1aof FIG. 6 did not allow CH₄ to dissolve at levels observed in analogouspolymers of monomers 1b and 1c of FIG. 6, as there was most likely verylittle free volume for it to fit within the compact and ionic structure.

This large solubility selectivity was not present in poly(RTIL)membranes made from monomers 1b and 1c of FIG. 6, where CO₂/CH₄solubility selectivity returned to levels typically found in bulk fluidRTILs. However, those poly(RTIL) membranes did also exhibit favorablediffusion selectivity for CO₂/CH₄. In the case of this poly(RTIL)-RTILcomposite, diffusion selectivity was expected to play a role in theseparation of CO₂/CH₄, as the poly(styrene) backbone has been successfulat slowing the diffusion of the larger CH₄ molecule regardless of theother chemical substituents present on the imidazolium cation bound tothe backbone. The presence of the RTIL component should lessen theCO₂/CH₄ solubility selectivity in the material, and is most likely thereason the composite poly(RTIL)-RTIL membrane exhibits lower CO₂/CH₄permselectivity than its counterpart membrane of monomer 1a, which lacksthe free ion pairs.

Example 3 Performance Relative to Other Poly(RTILs) and General PolymerMembranes

“Robeson Plots” are widely used for gauging the progress of polymer gasseparation membranes (Robeson L M, J. Memb. Sci. 1991; 62:165-185).These log-log charts plot ideal permselectivity for a gas pair againstthe ideal permeability of the more permeable gas. The “upper bound” canbe viewed as a target for researchers to exceed in the development ofnew membranes. The further to the upper right a material lies is oneindicator of its potential for industrial implementation (Baker, R W,Ind. Eng. Chem. Res. 2002; 41: 1393-1411). The “upper bound” hastraditionally been defined by glassy polymers with large diffusionselectivities (Robeson L M, J. Membr. Sci. 1991; 62:165-185; Freeman BD., Macromolecules 1999; 32: 375-380). In recent years, many polymers,especially those composed of polymers with polar linkages, such aspoly(ethylene glycol) (PEG) derivatives have exceeded the “upper bound”as they exhibit large solubility selectivities, while allowing for therapid permeation of each gas. The performance of the compositepoly(RTIL)-RTIL membrane and other poly(RTIL) membranes are plotted on“Robeson Plots” for CO₂/N₂ and CO₂/CH₄ (FIGS. 8 and 9). In each chart,the performance increase of the membrane formed from the poly(RTIL) ofmonomer 1a and the poly(RTIL)-RTIL composite is indicated by the redarrow.

Poly(RTIL) membranes have obviously fared better in CO₂/N₂ separations,as the positions of each material lie at or above the “upper bound”. InCO₂/CH₄ separation, they fall short of the mark, but the poly(RTIL)-RTILcomposite membrane represents an improvement over past poly(RTILs) inthis application, as the materials are approaching the “upper bound”.However, these poly(RTIL)-RTIL composites represent progress in bothseparations for imidazolium-based materials. These initial results withpoly(RTIL)-RTIL composites are very promising and suggest continued workon these materials in systematic studies to push CO₂ permeability higherwithout sacrificing to selectivity. Furthermore, as there are seeminglyinfinite combinations of poly(RTIL) and RTILs to be tested, there ishigh interest in identifying ideal candidate molecules forpoly(RTIL)-RTIL composite membranes. It is believed these resultsprovide an excellent set of tools to understand the chemical andphysical factors that can be utilized to drive and improve gasseparations in poly(-RTIL)-based membranes.

Example 4 Preparation of Additional Poly(RTIL)-RTIL Composite Membranes

A systematic study of poly(RTIL)-RTIL composite gas separation membraneswas performed, examining the effect of anion in the “free” RTILcomponent on the gas permeability and selectivity of poly(RTIL) matricesfabricated from the monomer 1d of FIG. 10 and a variety of [C₂mim][X]salts at 20 mol % (FIG. 12).

The RTIL monomer 1d depicted in FIG. 10 (2.50 g, 47.5 mmol) and a[C₂mim][X-] RTIL of interest were mixed in a 4:1 molar ratio, and themixture homogenized on a vibrating mixer. Divinylbenzene (0.0325 g, 2.50mmol) was then added, and the mixture homogenized again. Finally, aphotoinitiator, 2-hydroxy-2-methylpropiophenone (0.0250 g, 0.152 mmol),was added and the mixing step repeated a final time. The solution wascast on to a 50 cm×50 cm piece of porous poly(ether sulfone) support(Supor 200, Pall, Ann Arbor, Mich.) on top of a Rain-X-coated quartzplate. Rain-X is a commercially available, hydrophobic coating for glasssurfaces, which aids in the removal of the film after thephotopolymerization is completed. A second, identical quartz plate wasplaced on top to spread the monomer completely through the support withexcess flowing beyond the support but remained within the quartz plates.The plates were placed under a 365 nm UV light for 30 min. After thistime, the plates were separated with a clean razor blade. The supportedarea was liberated from the freestanding polymer. The support was cutwith a 47 mm diameter stainless steel die. The freestanding section wascollected for determining polymer density. Membrane thicknesses rangedfrom 150 to 190 μm. No phase separation between the poly(RTIL) and“free” RTIL components has been observed after storing these membranesat ambient conditions for several months.

Densities of poly(RTIL)-RTIL composites were determined using astraightforward, volumetric method. Approximately 1.00 g of compositewas added to a 10.00±0.02 mL, Class A volumetric flask of known mass.The mass of the polymer was recorded and hexanes (mixture of isomers)were added to the flask, and the mass of hexanes added was noted. Thevolume of hexanes added was calculated from its density (0.672 g/mL at25° C.) and that value subtracted from the volume of the empty flask.The difference was taken to be the volume of the composite. The densityof the composite was taken as the quotient of its mass and volume.Physical properties for each RTIL used and the densities of neatpoly(1d) and the four composites studied are presented below (Table 3).

TABLE 3 Physical Properties of RTILs and Densities of Poly(RTIL)Composites composite density MW Vm density Cation anion (g/cm³) (g/mol)(cm³/mol) (g/cm³) [C₂mim] Tf₂N 1.52 391.31 257 1.32 dca 1.08 177.21 1641.27 OTf 1.36 260.23 191 1.33 SbF₆ 1.85 346.92 188 1.52 poly(1d) 1.29

Single-gas permeation experiments using CO₂, N₂, and CH₄ were carriedout at 295 K using a time-lag apparatus. Construction and operation ofthis equipment have been detailed in our previous works relating topoly(RTILs) and other polymer gas separation membranes. Experiments wereperformed with a driving force of approximately 2 atm upstream againstinitial vacuum downstream. Membranes were degassed under dynamic vacuum(<1 Torr) for 18-22 h between runs. LabView (National Instruments,Austin, Tex.) was utilized for automated data collection.

Example 5 Selecting Components for Poly(RTIL)-RTIL Composites

Monomer 1d of FIG. 10 was chosen as the polymerizable component for thisstudy, as poly(RTIL) membranes made from this monomer were previouslyshown to exhibit CO₂ permeability of 16 barrers, with improved CO₂/N₂and CO₂/CH₄ selectivity relative to poly(RTILs) with alkyl substituents.Relative to all of the other “neat” poly(RTIL) gas separation membranes,poly(1d) had the best combination of properties for CO₂ separations, andthus, it was selected as the matrix for further studies on compositesystems. The anion, X, associated with the “free” imidazolium salt hasbeen shown to have a dramatic effect on the gas separation properties of[C₂mim]-based RTILs. RTILs with smaller anions, such as triflate (OTf)and dicyanamide (dca), improve CO₂/N₂ and CO₂/CH₄ ideal solubilityselectivities relative to those with Tf₂N anions (no data have beenreported yet for RTILs containing the SbF₆ anion). This behavior hasbeen explained as a function of molar volume through the use of regularsolution theory. Imidazolium-based RTILs with smaller molar volumes havegreater solubility selectivity for CO₂ relative to N₂ and CH₄. However,the solubility of CO₂ is greater in RTILs with larger molar volumes, andthis is also well-explained by RST.

Synthesis of RTIL-based monomers containing anions other than Tf₂N ismore challenging, as the ion exchange and purification ofimidazolium-based salts with anions such as OTf, dca, BF₄, etc., is lessconvenient. Several imidazolium-based monomers with these types ofanions have been reported to exist as solids at room temperature. Assolid monomers are more difficult to process into thin films forsubsequent photopolymerization, only imidazolium-based monomers thatexist as molten salts at ambient conditions have been used infabricating poly(RTILs). Thus, the effects of various anions on the gasseparation properties of poly(RTIL) membranes have not yet beenexplored. Use of poly(RTIL)-RTIL composites allows for the inclusion ofanions other than and in addition to Tf₂N in poly(RTIL)-based membranes,providing a means to study various anions within poly(RTIL) gasseparation membranes. In mixed anion poly(RTIL)-RTIL composites, the twoanionic species should not preferentially associate with the cationsbound to the polymer chain or the “free” cations. “Free” RTILs wereincluded at 20 mol % relative to the polymerizable RTIL so as to keepthe polymer as the major component of the membrane and determine theeffects that small amounts of “free” RTILs might have on the performanceof these membranes.

Example 6 Ideal Gas Permeability and Selectivity in Poly(RTIL)-RTILComposite Membranes

Table 4 presents the ideal permeabilities of CO₂, N₂, and CH₄ as well asthe ideal separation factors for CO₂/N₂ and CO₂/CH₄ in neat poly(1d) ofFIG. 10 and in composites of poly(1d) with four [C₂mim][X] RTILs. Idealselectivities were calculated as the ratio of ideal permeabilities.

TABLE 4 Ideal Gas Permeabilities and Selectivities in CompositeMembranes Ideal Selectivity Ideal Permeability (barrers) CO₂/ CO₂/Membrane CO₂ N₂ CH₄ N₂ CH₄ poly(1d) 16 ± 1 0.39 ± 0.02 0.48 ± 0.01 41 33poly(1d) Tf₂N 60 ± 2 1.7 ± 0.1 2.6 ± 0.1 36 24 with dca 41 ± 1 1.1 ± 0.11.6 ± 0.1 39 25 20 mol % OTf 43 ± 1 1.2 ± 0.1 21.7 ± 0.1  37 25 [C₂mim]SbF₆ 42 ± 1 1.1 ± 0.1 1.5 ± 0.1 39 27

Composite membranes exhibited gas permeabilities several times largerthan neat poly(1d) alone. The inclusion of “free” RTILs that are notcovalently bound to the polymer backbone should serve to increase gasdiffusion and, in turn, permeability, as solution diffusion is assumedto be the transport mechanism in these membranes according to theequation: P=SD

“Free” RTILs fill volume between polymer chains, creating domains wheregases may diffuse more rapidly than in poly(RTIL) matrices without“free” RTILs present. This behavior is akin to plasticization effects inmembranes made from traditional polymers, where the inclusion of aplasticizer (i.e., water, organic solvent, or gas) can increase the gasdiffusion and permeability of the membrane. However, the interactionsoccurring in poly(RTIL)-RTIL composites are unlike traditional polymersand plasticizers, as “free” RTILs are nonvolatile and are held withinthe poly(RTIL) matrix by ionic forces, thus severely limiting theirability to escape.

The inclusion of “free” [C₂mim][Tf₂N] had the most dramatic effect ongas permeability in these composite membranes. In the composite membranecontaining 20 mol % [C₂mim][Tf₂N], permeabilities for CO₂, N₂, and CH₄increased relative to neat poly(1d) by factors of 275%, 335%, and 440%,respectively, while those same gases exhibited average increases of155%, 210%, and 233% in the other three composites. As [C₂mim]-[Tf₂N]has the largest molar volume of the four RTILs included in the compositemembranes (Table 3), it may be occupying more space between polymerchains and enabling more rapid gas diffusion through the composite. Themolar volumes of the other [C₂mim][X] salts are similar to each otherand less than that of [C₂mim][Tf₂N], and those composites all exhibitedvery similar gas permeabilities of ca. 42 barrers. This work indicatesthat the molar volume of the “free” RTIL incorporated in thesepoly(RTIL)-RTIL composite gas separation membranes correlates quite wellwith gas permeability.

The nature of the “free” RTIL had a much smaller effect on the idealseparation selectivities of the composite membranes. While each of thecomposite poly(RTIL)-RTIL membranes had ideal selectivities for CO₂/N₂and CO₂/CH₄ less than that of neat poly(1d), little difference inseparation performance exists between the various composites. Gas pairselectivities ranged from 36 to 39 for CO₂/N₂ and 24 to 27 for CO₂/CH₄,with the composites containing [C₂mim][Tf2N] and [C₂mim][SbF₆],respectively, at the minima and maxima of those ranges. The selectivitydata of SILMs containing three of the RTILs for CO₂/N₂ and CO₂/CH₄separations have previously been reported and is summarized in Table 5.

TABLE 5 Ideal Selectivity Data Previously Reported for [C₂mim][X] SILMsideal selectivity SILM CO₂/N₂ CO₂/CH₄ [C₂mim] Tf₂N 20 11 dca 61 20 OTf35 N/A

With the exception of neat [C₂mim][dca] in ideal CO₂/N₂ separations,poly(RTIL)-RTIL composites containing these RTILs as “free” ion pairsexceed the selectivities of those SILMs. Separation of CO₂, N₂, and CH₄in SILMs is primarily achieved through solubility differences, withdiffusion selectivity having little or no impact on the separation ofthese gases. SILMs have much higher permeabilities than poly(RTILs), asdiffusion through a dense liquid film is much faster than that through adense solid. In polymer membranes, diffusion differences also often playa significant role in separation. Poly(RTIL) membranes have previouslyshown to exhibit favorable solubility and diffusion differences forCO₂/CH₄ separation. CO₂/N₂ separation was also favored by a largesolubility difference between the two gases but was hindered by theslightly more rapid diffusion of N₂. Poly(RTIL)-RTIL composites arehybrids with properties of both classes of materials. Permeability isincreased relative to a neat poly(RTIL) with the presence of “free”RTIL, yet the polymer component can still impart a diffusion separationselectivity mechanism that is not available with SILMs. Poly(RTIL)-RTILcomposites offer a highly modular membrane platform with tailoredchemistry and tunable gas permeability and selectivity.

Example 7 Performance of Poly(RTIL)-RTIL Composites Relative to OtherPolymer Membranes

As the ideal selectivities of the membrane with the highest permeabilityare only slightly less than those of membranes with lowerpermeabilities, a minimal “flux-selectivity tradeoff” exists in thesepoly(RTIL)-RTIL composites. This is due to the inherent selectivities ofboth the poly(RTIL) and “free” RTIL components in CO₂/N₂ and CO₂/CH₄,allowing for increasing permeability without sacrifice to selectivity.This is a very unique and powerful feature of poly(RTIL)-RTIL compositesand their use as gas separation membranes.

“Robeson plots” are a widely used metric for evaluating and visualizingthe progress in membrane science. These charts plot gas pair selectivityagainst the permeability of the membrane to one of the gases. Polymersthat lie closer to the top right quadrant are potentially more viablefor use in industrial processes. An apparent “upper bound” exists on thechart that was traditionally defined by glassy membranes with largediffusion selectivities. Parts a and b of FIG. 13 are “Robeson plots”for CO₂/N₂ and CO₂/CH₄ annotated to include poly(RTIL)-RTIL composites.

These “Robeson plots” indicate the CO₂/N₂ is a more favorable separationthan CO₂/CH₄ for poly(RTIL)-RTIL composite gas separation membranes.Poly(RTIL)-RTIL composite membranes lie above the “upper bound” forCO₂/N₂ separation, indicating they are superior to many other polymermembranes for this application. The fact that poly(RTIL)-RTIL compositescontinue to positively deviate from this line gives promise to thepursuit of future research with these materials. It is not surprisingthat CO₂/CH₄ separation remains below the “upper bound” inpoly(RTIL)-RTIL composite membranes, as our previous models and datasuggest that RTIL-based systems are much less likely to outperform thebest polymer materials for this separation.

Poly(RTIL)-RTIL composite membranes containing 20 mol % of a “free” RTILwere fabricated from readily synthesized and/or commercially availablecomponents. The permeabilities of membranes to CO₂, N₂, and CH₄ weredetermined. The inclusion of a “free” RTIL component was found toincrease the permeability of each gas by approximately 2-4 time that ofan analogous polymer membrane without a “free” RTIL component. Gaspermeability was greatest in the composite membrane that contained the“free” RTIL with the largest molar volume. Poly(RTIL)-RTIL compositemembranes exhibited ideal gas separation selectivities slightly lessthan an analogous polymer without a “free” RTIL component but werehigher than what can be achieved in most SILMs. When viewed on “Robesonplots”, poly(RTIL)-RTIL composite membranes exceeded the “upper bound”for CO₂/N₂ separation but fall short for CO₂/CH₂. While poly(RTIL)-RTILcomposites are approximately an order of magnitude less permeable thansome SILMs, much room remains for improvement.

During the course of these and other experiments, no phase separationbetween poly(RTIL) and RTIL components has been observed. The appliedpressure of approximately 2 atm was not sufficient to separate the“free” RTIL from the poly(RTIL) component. Ionic interactions appear tohold the “free” RTIL within the polymer matrix, preventing its releasewhere a typical SILM would fail. It is anticipated that the strength ofsuch interactions are quite strong and that applied pressure alone willnot be sufficient to separate the RTIL from the poly(RTIL) matrix.

Example 8 Effect of Amount of Unpolymerized RTIL on Membrane Properties

To investigate the effect of the amount of unpolymerized RTIL had on thepermeability and selectivity of composite membranes, thin film membraneswere constructed using an unpolymerized RTIL [C2mim] present in amountsfrom 0%, 20%, 40% and 60% by weight. The following polymerizable styrenemonomer and vinyl monomer were used as the poly(RTILs):

The styrene or vinyl monomer was added to a [C₂mim][Tf2N] mixture andthen stirred overnight (12-24 hours). Subsequently, a crosslinker,divinylbenzene (0.0132 g) and a photoinitiator,2-hydroxy-2-methylpropiophenone (0.01 g) were added. Finally, themixture was homogenized on a vibrating mixer or stirred using a magneticstir bar. The solution was casted between two Rain-X®-coated glassplates. The membrane was then baked in an Ultraviolet crosslinker oven(CL-1000, UVP) for at least 6 hours.

Free standing membranes were obtained from these procedures, thecompositions of which are presented in Table 6. A membrane called bye.g. styrene (80-20), means that the membrane contains of 80 wt % of thestyrene polymer, and 20 wt % of [C₂mim][Tf₂N]. Vinyl (80-20) membranemeans that the membrane contains of 80 wt % of the vinyl polymer, and 20wt % of [C₂mim][Tf₂N]. The thickness of each membrane is shown in Table6.

TABLE 6 m [C₂mim][Tf2N] m poly(RTIL) Thickness Name (gram) (gram) (μm)Styrene (80-20) 0.4 1.6 — Styrene (60-40) 0.8 1.2 142 Styrene (40-60)1.2 0.8 142 Vinyl (100) — 2.0 142 Vinyl (80-20) 0.4 1.6 142 Vinyl(40-60) 1.2 1.8 142

Single-gas permeation experiments using CO₂, CH₄, and N₂ (99.99% purity,Airgas) were performed at 296 K using a time-lag apparatus. Theexperiments were conducted with a driving force of 1 to 1.5 atm in theupper stream, and vacuum on the downstream. All fresh membranes weretypically degassed under dynamic vacuum (<1 Torr) overnight (˜12 hours),and then degassed for at least 20 hours between each run. The steadystate permeability was calculated using the steady state flux. The idealselectivity is calculated by the ratio of the permeability of the fasterpermeating gas over the slower one.

The CO₂, N₂ and CH₄ permeability and CO₂/CH₄ and CO₂/N₂ selectivity ofall the styrene and vinyl based poly(RTIL) membranes are presented inTables 7 and 8 respectively. Tables 7 and 8 present the selectivity andpermeability of the membranes with respect to the different gasses. Theselectivity and permeability for neat [C2mim][Tf₂N] and the styrenepoly(RTIL) without [C₂mim][Tf₂N] were known from previous experiments.

TABLE 7 P CO₂ P N₂ P CH₄ Name (barrers) (barrers) (barrers) P CO₂/N₂ PCO₂/CH₄ Styrene (100-0) 9.2 0.3 0.2 32.0 39.0 Styrene (80-20) 44.0 1.11.6 39.0 27.0 Styrene (60-40) 108.1 3.1 4.9 35.0 22.0 Styrene (40-60)257.3 8.0 12.9 32.0 20.0 Styrene (0-100) 686 22 48 31.2 14.3

TABLE 8 P CO₂ P N₂ P CH₄ Name (barrers) (barrers) (barrers) P CO₂/N₂ PCO₂/CH₄ Vinyl (100-0) 67.3 4.6 6.3 14.5 10.6 Vinyl (80-20) 97.3 5.1 8.819.1 11.1 Vinyl (40-60) 285.8 13.4 20.8 21.3 13.8 Vinyl (0-100) 686 2248 31.2 14.3

As shown in Tables 7 and 8, increasing the amount of the unpolymerizedRTIL increases the permeability of the membrane for each gas. Increasingthe amount of the unpolymerized RTIL significantly lowered theselectivity for CO₂/CH₄ for the styrene poly(RTIL), but had less of aneffect for CO₂/N₂ selectivity and for the vinyl poly(RTIL). Themembranes made from the vinyl poly(RTIL) generally had higherpermeability but slightly lower selectivity.

Example 9 Synthesis of an Ammonium-Based Ionene

Ammonium-based ionenes were synthesized by reacting a N,N,N′,N′tetramethylalkyldiamine with a dibromoalkane (Scheme 1). Reactions weredone in a minimal amount of methanol to keep the reactants and productsin solution (25-50 wt %). Reactions were carried out at reflux for 1-5days. Specifically N,N,N′,N′-tetramethylhexanediamine was reacted withdibromohexane in methanol at reflux for 48 hours. The polymer was thenion exchanged from Br⁻ to Tf₂N⁻. The polymer was dissolved in water anda solution of LiTf₂N was slowly added. The ion exchanged polymer quicklycrashed out and was left to stir for 24 hours. The solids were thenfiltered. Composites of the anion-exchanged ionene were then blendedwith RTIL. Specifically [C₆mim][Tf₂N] and [N₈₁₁₁][Tf₂N]. A specificamount of ionene and RTIL were dissolved in a minimal amount of DMSO ina evaporation dish. Once completely dissolved, the solution was heatedto 100° C. and the DMSO was allowed to evaporate at atmospheric pressurefor about 4 hours or until most all the DMSO has evaporated. The samplewas then placed in a vacuum oven and the remaining DMSO was pulled off.The resulting material was a solid homogeneous material. Composite weremade with RTIL with 20-50% [C₆mim][Tf₂N] and 50% ammonium RTIL.

Example 10 Surface Resistivity Measurements for Use as AntistaticMaterials

A polymer film generated as shown in Scheme 2 (R1=R2=(CH₂)₁₀, Z1=Z2=H,Y=CH₃, X=Br) was tested for static dissipative and antistaticcapabilities. Surface resistance was measured with Monroe Electronics,Model 272A Surface Resistance Meter and probe setup as provided. Themeasurement apparatus was able to determine surface resistivity at 10Vand 100V, both voltages of which were measured. Film was used asprovided for the surface resistivity testing.

The antistatic film was placed on top of the insulated sample plate andpermitted to equilibrate for approximately 30 minutes. The wiringbetween the meter and the probe was connected. The probe electrodeprotective cap was removed and the electrode surfaces were examined forcontamination and cleaned per instructions. The meter was switched onand also permitted to equilibrate for approximately 30 minutes prior tocollecting data. The meter was switched to the 10 V setting for initialanalysis. The probe provides a fixed weight, constant pressure to thesurface of the film to maintain the electrode contact on the surface ofthe film during measurement. No additional force was applied other thanwhat the weighted probe provides. The probe was then placed on top ofthe film and the measurement taken when the resistance value stabilizedwhich was typically 3 to 5 seconds after placing the probe on the filmsurface. Between measurements the film was turned over, the probereplaced and a new measurement taken. Each time the probe wasrepositioned the film/electrode interface was examined to ensure thatthe electrode surfaces were in complete contact with the film. Uponcompletion of the measurement of at the 10 V level, the meter was resetto 100 V and the measurement process repeated. The collected data islisted below in Table 9.

TABLE 9 Surface resistivity of poly(RTIL) materials, 10 V and 100 V.Surface Resistivity Reading (ohms/cm²) 10 V Potential 1   5.1 × 10⁹ 2  5.1 × 10⁹ 3   4.9 × 10⁹ Avg.   5.0 × 10⁹ Std Dev ±1.2 × 10⁸ 100 VPotential 1   4.3 × 10⁹ 2   4.4 × 10⁹ 3   4.2 × 10⁹ Avg.   4.3 × 10⁹ StdDev ±1.0 × 10⁹

As is seen from the data, the poly(RTIL) polymer has surface resistivitysuitable for an antistatic agent, i.e., greater than 10⁹. The antistaticmaterials of the present invention can be used as surface coatings(which are sprayed or otherwise applied to a surface), surfacelaminates, or additives blended into the base polymer or substratematerial. The poly(RTIL) materials are less corrosive, have improvedoptical clarity, can meet FDA and USP approval for use around food andmedical devices, and additionally can be produced at a lower cost thantypical antistatic materials. The poly(RTIL) materials also have ahigher temperature processability for polymers like polycarbonate,nylon, polyurethane, polyimide/amides. Furthermore, the structures ofthe poly(RTIL) and poly(RTIL)-RTIL composites can be modified to ensurecompatibility with the host polymer or substrate while minimizing anyimpact of the properties of the host polymer or substrate.

Example 11 Water Miscibility of Vicinal Diol-FunctionalizedImidazolium-Based RTILS

Vicinal diol-functionalized, imidazolium-based RTILs containing the Tf₂Nanion were selected because this anion does not form HF and often leadsto RTILs with more favorable properties (e.g., lower viscosity, higherthermal stability). It was found that by varying the length of then-alkyl group on these diol-functionalized alkylimidazolium RTILs, theirmiscibility in water can be adjusted to be completely water miscible orimmiscible.

The Tf₂N anion has been described as a hydrophobic RTIL anion, althoughmany Tf₂N-containing RTILs are somewhat hygroscopic. For this reason, itwas surprising when certain imidazolium-based RTILs containing vicinaldiol-functionalized cations and Tf₂N anions (RTILs 7 and 9 in Scheme 5)were completely miscible with water. Furthermore, it was determined thatthe water-miscibility of these RTILs could be controlled by changing thelength of the N-alkyl group on the cation or varying substitution at the2-position of the imidazolium cation core.

Curiosity about these diol-RTILs was driven by the attempted anionexchange of 1-(2,3-dihydroxypropyl)-3-methylimidazolium chloride (RTIL 1in Scheme 4) to the Tf₂N anion using typical aqueous procedures whichdid not produce a water immiscible precipitate, as has come to beexpected from imidazolium-based RTILs with Tf₂N anions. This unusualresult prompted the synthesis of derivatives 7-12 in Scheme 5 withvarying substitution of R and R′. Compounds 1-6 were prepared inexcellent yield by stirring 1-chloro-2,3-propanediol with thecorresponding imidazole reagent at 130° C. for 48 hours (Scheme 4). Thereaction was attempted using various solvents (EtOH, CH₃CN, toluene) atreflux and was incomplete after several days. However, N-alkylationproceeded most effectively as a neat (solvent-free) reaction. Thereaction mixture was then placed under dynamic vacuum (<1 torr) at 130°C. for another 48 hours to remove any residual starting materials. Priorsyntheses of RTILs containing the same cation were conducted inrefluxing toluene and required repeated washing with CH₃CN, while ourmethods require no additional organic solvents. All of the imidazoliumchloride salts were water-miscible, viscous, brown-colored oils exceptRTIL 2, which was a solid. The products were carried on without furtherpurification as they were quite pure as confirmed by ¹H NMR analysis.

Scheme 4

RTIL R R′ Yield 1 Me H 100% 2 Me Me 100% 3 Et H  94% 4 Pr H  95% 5 Bu H 92% 6 Bn H  97%

The chloride salts were then ion-exchanged to give the correspondingTf₂N-containing RTILs 7-12 (Scheme 5), all of which were slightlyviscous, brown liquids. The choice of Tf₂N anion source and solvent forthis reaction were determined by the water miscibility of the finalproduct. The water immiscible RTILs 8, and 10-12 were produced usingstandard conditions with LiTf₂N in water. Upon mixing, the RTILs formeda separate layer from water and were diluted with EtOAc and washedrepeatedly with water until qualitatively halide free (as confirmed bylack of a precipitate upon addition of AgNO₃ to the aqueous washings).The water-miscible RTILs (7 and 9) were prepared using CH₃CN as thesolvent and KTf₂N. KTf₂N was chosen because lithium salts often haverelatively high solubilities in organic solvents, which could lead toresidual Li-containing impurities. The final products were isolated byfiltering the KCl by-product and evaporation of the solvent underdynamic vacuum at 65° C. RTIL 11 was also prepared using the KTf₂N/CH₃CNprotocol and found to still be water immiscible, indicating that thesolubility properties of these RTILs are independent of the method usedto produce them.

Scheme 5

RTIL R R′ Solvent/M Yield H₂O Miscible  7 Me H CH₃CN/K 100% Yes  8 Me MeH₂O/Li  64% No  9 Et H CH₃CN/K 100% Yes 10 Pr H H₂O/Li  60% No 11 Bu HH₂O/Li  44% No 12 Bn H H₂O/Li  95% No

1-(2,3-Dihydroxypropyl)-3-alkylimidazolium Tf₂N RTILs with N-alkylgroups larger than ethyl (RTILs 10-11) were immiscible with water (i.e.,they form a separate layer when mixed with water) at ambienttemperature. The same behavior was observed when the alkyl chain isreplaced with a benzyl group (RTIL 12). Increasing the hydrophobicity ofthe cation by increasing the hydrocarbon content renders the RTILproduct water-immiscible. Replacing the proton at the 2-position of theimidazolium cation with a methyl group (RTIL 8) gives a RTIL that is notmiscible with water, while the protio analog (RTIL 7) is miscible.Whether the increased hydrophobicity of RTIL 8 is due simply to higherhydrocarbon content by adding the methyl group or a more complexmechanism involving effects of substitution at the 2-position on theimidazolium ring is not clear at this time, and is beyond the scope ofthis work.

It has been previously reported that the hydrophilicity of an RTIL canbe adjusted by mixing it with water-soluble, inorganic salts (e.g.,K₃PO₄). To ensure that the unique behaviors of RTILs 7 and 9 were aresult of the cation structure and not ionic impurities, they wereanalyzed for potassium (K⁺) and chloride (Cl⁻) ion content. K⁺ analysiswas conducted using an inductively coupled plasma (ICP) instrument, andCl⁻ analysis by ion chromatography (IC). The residual K⁺ contents of 7and 9 were 680 and 610 ppm, and Cl⁻ concentrations were 104 and 71 ppm,respectively. Because these values are quite low, the water miscibilityof the RTIL can be attributed to the nature of the cation and notinorganic salt impurities. Additionally, the water content of RTILs 7-12was determined by Karl Fischer titration to be less than 500 ppm in allcases.

It appears that the vicinal diol functional group on the cation wasessential to the water miscibility of these RTILs. AnotherTf₂N-containing imidazolium salt 13 (Scheme 6) with two alcohol groupson the cation was synthesized and found to be water immiscible. Thesymmetric imidazolium salt 13 is a constitutional isomer of RTIL 7, yetdisplays very different properties. This indicates that the miscibilityof RTILs 7 and 9 is not due simply to increased polarity by addingmultiple OH groups to the cation. The vicinal diol functionality has aunique effect on the miscibility of RTILs. Without wishing to be boundby any particular belief, the enhanced miscibility may be a consequenceof enhanced hydrogen-bonding with water.

In conclusion, a series of six new imidazolium-Tf₂N RTILs with a vicinaldiol-substituted cation were prepared. It was found that the length ofthe alkyl substitution on the cation dictated the water miscibility ofthe RTIL, with methyl and ethyl substitution producing RTILs that werecompletely miscible in water, and longer alkyl homologues affordingcompletely water-immiscible RTILs. Some imidazolium-based RTILs with aTf₂N anion were found to be completely water-miscible, and can havetheir water miscibility properties adjusted by systematic cationmodifications. These RTILs may find utility in various applications asthey are water-miscible but do not incorporate a traditional“hydrophilic” anion. Also see LaFrate et al., Industrial and EngineeringChemistry Research (2009), 48(19), 8757-8759, which is herebyincorporated by reference.

Example 11 Detailed Synthesis Information of Certain RTIL Compounds

The RTIL compounds of Example 10 were prepared as described below.Unless otherwise noted, all reagents were purchased from commercialsuppliers and were used without further purification, with the exceptionof 1-ethyl- and 1-propylimidazole, which were prepared following aliterature procedure (Bara et al Ind. Eng. Chem. Res. 2007, 46,5397-5404). ¹H NMR spectra were recorded on a 400 MHz Varian instrumentand ¹³C NMR were recorded at 100 MHz on the same instrument. NMR spectraare reported in ppm and were referenced to the solvent peak andprocessed using ACD Labs 5.0 software. ESI mass spectra were recordedusing the Applied Biosystems QSTAR Hybrid LC/MS/MS System massspectrometer. K⁺ content was determined using an Applied ResearchLaboratories 3410+ inductively coupled plasma-optical emissionspectrometer. Cl⁻ content was determined using a Dionex Series 4500i IonChromatograph. Water content was measured using a Mettler Toledo DL32Karl Fischer Coulometer. Elemental analyses were conducted by GalbraithLaboratories (Knoxville, Tenn.)

1-(2,3-Dihydroxypropyl)-3-methylimidazolium Chloride (RTIL 1)

1-Methylimidazole (8.21 g, 100 mmol) and 3-chloro-1,2-propanediol (11.05g, 100.0 mmol) were stirred in a 130° C. oil bath for 48 h, after whichthe flask was placed under vacuum and stirring continued at 130° C. foranother 48 h. The residue was then dissolved in CH₃OH, transferred to atared flask and concentrated to afford the product as a viscous brownoil (19.3 g, 100%). ¹H NMR: δ_(H) ppm (400 MHz; DMSO-d₆) 3.19-3.29 (m,1H) 3.36-3.48 (m, 1H) 3.77 (dd, J=6.78, 4.21 Hz, 1H) 3.87 (s, 3H) 4.10(dd, J=13.74, 7.69 Hz, 1H) 4.32 (dd, J=13.74, 3.11 Hz, 1H) 5.13 (br. s.,1H) 5.53 (d, J=5.13 Hz, 1H) 7.72 (t, J=1.74 Hz, 1H) 7.74 (t, J=1.74 Hz,1H) 9.18 (s, 1H).

1-(2,3-Dihydroxypropyl)-2,3-dimethylimidazolium Chloride (RTIL 2)

1,2-Dimethylimidazole (9.61 g, 100 mmol) and 3-chloro-1,2-propanediol(11.05 g, 100.0 mmol) were stirred in a 130° C. oil bath for 48 h, afterwhich the flask was placed under vacuum and stirring continued at 130°C. for another 48 h. The product was then stirred in refluxing ether for24 h and filtered to afford a brown solid (20.29 g, 100%). ¹H NMR: δ_(H)ppm (400 MHz; DMSO-d₆) 2.60 (s, 3H) 3.20-3.33 (m, 1H) 3.36-3.49 (m, 2H)3.78 (s, 3H) 4.08 (dd, J=14.11, 7.88 Hz, 1H) 4.27 (dd, J=14.11, 3.11 Hz,1H) 5.14 (t, J=5.50 Hz, 1H) 5.50 (d, J=5.68 Hz, 1H) 7.63 (d, J=2.01 Hz,1H) 7.66 (d, J=2.20 Hz, 1H).

1-(2,3-Dihydroxypropyl)-3-ethylimidazolium Chloride (RTIL 3)

1-Ethylimidazole (2.40 g, 25.0 mmol) and 3-chloro-1,2-propanediol (2.76g, 25.0 mmol) were stirred in a 130° C. oil bath for 48 h, after whichthe flask was placed under vacuum and stirring continued at 130° C. foranother 48 h. The residue was then dissolved in CH₃OH, transferred to atared flask and concentrated to afford the product as a viscous brownoil (4.88 g, 94%). ¹H NMR: δ_(H) ppm (400 MHz; DMSO-d₆) 1.41 (t, J=7.24Hz, 3H) 3.23 (dd, J=11.17, 6.96 Hz, 1H) 3.37-3.47 (m, 1H) 3.70-3.86 (m,1H) 4.11 (dd, J=13.74, 7.69 Hz, 1H) 4.22 (q, J=7.33 Hz, 2H) 4.33 (dd,J=13.74, 3.11 Hz, 1H) 5.19 (br. s., 1H) 5.59 (br. s., 1H) 7.78 (t,J=1.74 Hz, 1H) 7.85 (t, J=1.74 Hz, 1H) 9.33 (t, J=1.56 Hz, 1H).

1-(2,3-Dihydroxypropyl)-3-propylimidazolium Chloride (RTIL 4)

1-Propylimidazole (2.75 g, 25.0 mmol) and 3-chloro-1,2-propanediol (2.76g, 25.0 mmol) were stirred in a 130° C. oil bath for 48 h, after whichthe flask was placed under vacuum and stirring continued at 130° C. foranother 48 h. The residue was then dissolved in CH₃OH, transferred to atared flask and concentrated to afford the product as a viscous brownoil (5.20 g, 95%). ¹H NMR: δ_(H) ppm (400 MHz; DMSO-d₆) 0.84 (t, J=7.42Hz, 3H) 1.74-1.86 (m, 2H) 3.22 (dd, J=11.17, 6.96 Hz, 1H) 3.42 (dd,J=10.99, 4.95 Hz, 1H) 4.07-4.20 (m, 3H) 4.33 (dd, J=13.74, 3.11 Hz, 1H)5.15 (br. s., 1H) 5.56 (br. s., 1H) 7.78 (t, J=1.74 Hz, 1H) 7.82 (t,J=1.83 Hz, 1H) 9.29 (t, J=1.47 Hz, 1H).

1-(2,3-Dihydroxypropyl)-3-butylimidazolium Chloride (RTIL 5)

1-Butylimidazole (12.42 g, 100.0 mmol) and 3-chloro-1,2-propanediol(11.05 g, 100.0 mmol) were stirred in a 130° C. oil bath for 48 h, afterwhich the flask was placed under vacuum and stirring continued at 130°C. for another 48 h. The residue was then dissolved in CH₃OH,transferred to a tared flask, and concentrated to afford the product asa viscous brown oil (23.27 g, 92%). ¹H NMR: δ_(H) ppm (400 MHz; DMSO-d₆)0.89 (t, 3H) 1.17-1.31 (m, 2H) 1.69-1.83 (m, 2H) 3.19-3.28 (m, 1H)3.37-3.46 (m, 1H) 3.78 (dd, J=7.05, 4.49 Hz, 1H) 4.12 (dd, J=13.83, 7.60Hz, 1H) 4.20 (t, J=7.14 Hz, 2H) 4.33 (dd, J=13.74, 3.11 Hz, 1H) 5.16(br. s., 1H) 5.56 (d, J=5.31 Hz, 1H) 7.78 (t, J=1.74 Hz, 1H) 7.83 (t,J=1.74 Hz, 1H) 9.30 (t, J=1.47 Hz, 1H).

1-(2,3-Dihydroxypropyl)-3-benzylimidazolium Chloride (RTIL 6)

1-Benzylimidazole (3.95 g, 25.0 mmol) and 3-chloro-1,2-propanediol (2.76g, 25.0 mmol) were stirred in a 130° C. oil bath for 48 h, after whichthe flask was placed under vacuum and stirring continued at 130° C. foranother 48 h. The residue was then dissolved in CH₃OH and transferred toa tared flask and concentrated to afford the product as a viscous brownoil (6.50 g, 97%). ¹H NMR: δ_(H) ppm (400 MHz; DMSO-d₆) 3.18-3.30 (m,1H) 3.37-3.49 (m, 1H) 3.73-3.86 (m, 1H) 4.15 (dd, J=13.74, 7.69 Hz, 1H)4.36 (dd, J=13.74, 3.11 Hz, 1H) 5.21 (t, J=5.50 Hz, 1H) 5.49 (s, 2H)5.62 (d, J=5.50 Hz, 1H) 7.32-7.50 (m, 5H) 7.80 (t, J=1.83 Hz, 1H) 7.86(t, J=1.83 Hz, 1H) 9.49 (t, J=1.56 Hz, 1H).

1-(2,3-Dihydroxypropyl)-3-methylimidazoliumBis(trifluoromethanesulfonimide) (RTIL 7)

1-(2,3-Dihydroxypropyl)-3-methylimidazolium chloride (1, 1.71 g, 8.88mmol) and KTf₂N (2.83 g, 8.88 mmol) were stirred in CH₃CN (10 mL) for 24h, then filtered through Celite and concentrated to give an orange/brownoil (3.92 g, 100%). ¹H NMR: δ_(H) ppm (400 MHz; DMSO-d₆) 3.20-3.30 (m,1H) 3.43 (dd, J=10.90, 4.67 Hz, 1H) 3.77 (dd, J=6.69, 4.49 Hz, 1H) 3.86(s, 3H) 4.06 (dd, J=13.74, 8.06 Hz, 1H) 4.29 (dd, J=13.74, 2.93 Hz, 1H)4.95 (br. s., 1H) 5.33 (d, J=4.95 Hz, 1H) 7.66-7.69 (m, 2H) 9.05 (s,1H). ¹³C NMR: δ_(C) ppm (100 MHz; DMSO-d₆) 35.69, 52.17, 62.72, 119.51(q, CF₃, J=322.64 Hz), 123.17, 123.20, 137.09. HRMS: Calc'd forC₁₆H₂₆F₆N₅O₈S₂ [A⁺][A⁺][B⁻]: 594.1127. Found: 594.1096. ElementalAnalysis: Calc'd: C, 24.72%; H, 3.00%; N, 9.61%. Found: C, 24.54%; H,2.88%; N, 9.37%. H₂O content: 423 ppm.

1-(2,3-Dihydroxypropyl)-2,3-dimethylimidazoliumBis(trifluoromethanesulfonimide) (RTIL 8)

1-(2,3-Dihydroxypropyl)-2,3-dimethylimidazolium chloride (2, 4.13 g,20.0 mmol) and LiTf₂N (6.32 g, 22.0 mmol) were dissolved in water (50mL) and stirred for 24 h. The mixture was then diluted with EtOAc (100mL) and washed with water (5×25 mL) until no precipitate formed in theaqueous layer upon adding AgNO₃. The EtOAc layer was then dried overanhydrous MgSO₄, filtered, and concentrated to give the product as anorange/brown oil (5.87 g, 64%). ¹H NMR: δ_(H) ppm (400 MHz; DMSO-d₆)2.58 (s, 3H) 3.29 (dd, J=10.99, 6.59 Hz, 1H) 3.44 (dd, J=10.99, 4.95 Hz,1H) 3.76 (s, 4H) 4.04 (dd, J=14.56, 7.60 Hz, 1H) 4.23 (dd, J=14.29, 3.11Hz, 1H) 4.94 (br. s., 1H) 5.23 (br. s., 1H) 7.55 (d, J=2.20 Hz, 1H) 7.59(d, J=2.01 Hz, 1H). ¹³C NMR: δ_(C) ppm (100 MHz; DMSO-d₆) 9.62, 34.79,50.95, 62.85, 70.30, 119.69 (q, CF₃, J=317.42 Hz), 121.96, 122.14,145.18. HRMS: Calc'd for C₁₈H₃₀F₆N₅O₈S₂ [A⁺][A⁺][B⁻]: 622.1440. Found:622.1438. Elemental Analysis: Calc'd: C, 26.61%; H, 3.35%; N, 9.31%.Found: C, 26.12%; H, 2.98%; N, 9.11%. H₂O content: 443 ppm.

1-(2,3-Dihydroxypropyl)-3-ethylimidazoliumBis(trifluoromethanesulfonimide) (RTIL 9)

1-(2,3-Dihydroxypropyl)-3-ethylimidazolium chloride (3, 2.85 g, 13.8mmol) and KTf₂N (4.40 g, 13.8 mmol) were stirred in CH₃CN (10 mL) for 24h, then filtered through Celite and concentrated to give an orange/brownoil (6.25 g, 100%). ¹H NMR: δ_(H) ppm (400 MHz; DMSO-d₆) 1.42 (t, J=7.24Hz, 3H) 3.26 (dd, J=10.90, 6.69 Hz, 1H) 3.43 (dd, J=10.99, 4.95 Hz, 1H)3.77 (br. s., 1H) 4.06 (dd, J=13.74, 8.06 Hz, 1H) 4.21 (q, J=7.33 Hz,2H) 4.29 (dd, J=13.83, 3.02 Hz, 1H) 4.95 (br. s., 1H) 5.33 (br. s., 1H)7.70 (t, J=1.74 Hz, 1H) 7.78 (t, J=1.74 Hz, 1H) 9.12 (t, J=1.56 Hz, 1H).¹³C NMR: δ_(C) ppm (100 MHz; DMSO-d₆) 15.17, 44.16, 52.27, 62.78, 69.64,119.51 (q, CF₃, J=321.87 Hz), 121.68, 123.33, 136.29. HRMS: Calc'd forC₁₈H₃₀F₆N₅O₈S₂ [A⁴][A⁴][B]: 622.1440. Found: 622.1432. ElementalAnalysis: Calc'd: C, 26.61%; H, 3.35%; N, 9.31%. Found: C, 26.20%; H,3.08%; N, 9.03%. H₂O content: 452 ppm.

1-(2,3-Dihydroxypropyl)-3-propylimidazoliumBis(trifluoromethanesulfonimide) (RTIL 10)

1-(2,3-Dihydroxypropyl)-3-propylimidazolium chloride (4, 3.40 g, 15.4mmol) and LiTf₂N (4.85 g, 16.9 mmol) were dissolved in water (40 mL) andstirred for 24 h. The mixture was then diluted with EtOAc (100 mL) andwashed with water (5×25 mL) until no precipitate formed in the aqueouslayer upon adding AgNO₃. The EtOAc layer was then dried over anhydrousMgSO₄, filtered and concentrated to give the product as an orange/brownoil (4.27 g, 60%). ¹H NMR: δ_(H) ppm (400 MHz; DMSO-d₆) 0.85 (t, J=7.42Hz, 3H) 1.71-1.88 (m, 2H) 3.25 (dd, J=10.99, 6.78 Hz, 1H) 3.43 (dd,J=10.99, 4.95 Hz, 1H) 3.78 (br. s., 1H) 3.99-4.11 (m, 1H) 4.14 (t,J=7.05 Hz, 2H) 4.30 (dd, J=13.83, 3.02 Hz, 1H) 4.96 (br. s., 1H) 5.34(br. s., 1H) 7.71 (t, J=1.74 Hz, 1H) 7.77 (t, J=1.74 Hz, 1H) 9.12 (t,J=1.47 Hz, 1H). ¹³C NMR: δ_(C) ppm (100 MHz; DMSO-d₆) 10.37, 22.97,50.36, 52.32, 62.81, 69.67, 119.59 (q, CF₃, J=322.07 Hz), 122.00,123.43, 136.69. HRMS: Calc'd for C₂₀H₃₄F₆N₅O₈S₂ [A⁺][A⁺][B⁻]: 650.1753.Found: 650.1726. Elemental Analysis: Calc'd: C, 28.39%; H, 3.68%; N,9.03%. Found: C, 28.06%; H, 3.15%; N, 8.60%. H₂O content: 459 ppm.

1-(2,3-Dihydroxypropyl)-3-butylimidazoliumBis(trifluoromethanesulfonimide) (RTIL 11)

1-(2,3-Dihydroxypropyl)-3-butylimidazolium chloride (5, 5.09 g, 20.0mmol) and LiTf₂N (6.32 g, 22.0 mmol) were dissolved in water (50 mL) andstirred for 24 h. The mixture was then diluted with EtOAc (100 mL) andwashed with water (5×25 mL) until no precipitate formed in the aqueouslayer upon adding AgNO₃. The EtOAc layer was then dried over anhydrousMgSO₄, filtered, and concentrated to give the product as an orange/brownoil (4.27 g, 44%). ¹H NMR: δ_(H) ppm (400 MHz; DMSO-d₆) 0.90 (t, 3H)1.20-1.32 (m, 2H) 1.71-1.85 (m, 2H) 3.20-3.31 (m, 1H) 3.38-3.50 (m, 1H)3.71-3.85 (m, 1H) 4.07 (dd, J=13.83, 7.97 Hz, 1H) 4.18 (t, J=7.14 Hz,2H) 4.30 (dd, J=13.83, 3.02 Hz, 1H) 4.95 (br. s., 1H) 5.34 (d, J=5.13Hz, 1H) 7.70 (t, J=1.74 Hz, 1H) 7.77 (t, J=1.74 Hz, 1H) 9.12 (t, J=1.47Hz, 1H). ¹³C NMR: δ_(C) ppm (100 MHz; DMSO-d₆) 13.28, 18.83, 31.47,48.58, 52.29, 62.80, 69.64, 119.54 (q, CF₃, J=322.24 Hz), 121.98, 123.39136.68. HRMS: Calc'd for C₂₂H₃₈F₆N₅O₈S₂ [A⁺][A⁺][B⁻]: 678.2066. Found:678.2042. Elemental Analysis: Calc'd: C, 30.06%; H, 3.99%; N, 8.76%.Found: C, 29.94%; H, 3.83%; N, 8.47%. H₂O content: 379 ppm.

1-(2,3-Dihydroxypropyl)-3-benzylimidazoliumBis(trifluoromethanesulfonimide) (RTIL 12)

1-(2,3-Dihydroxypropyl)-3-benzylimidazolium chloride (6, 2.04 g, 7.60mmol) and LiTf₂N (2.40 g, 8.30 mmol) were dissolved in water (20 mL) andstirred for 24 h. The mixture was then diluted with EtOAc (100 mL) andwashed with water (5×25 mL) until no precipitate formed in the aqueouslayer upon adding AgNO₃. The EtOAc layer was then dried over anhydrousMgSO₄, filtered, and concentrated to give the product as an orange/brownoil (3.76 g, 95%). ¹H NMR: δ_(H) ppm (400 MHz; DMSO-d₆) 3.26 (dd,J=10.35, 7.05 Hz, 1H) 3.44 (dd, J=10.90, 4.85 Hz, 1H) 3.72-3.85 (m, 1H)4.10 (dd, J=13.92, 8.06 Hz, 1H) 4.32 (dd, J=13.74, 2.93 Hz, 1H) 4.96(br. s., 1H) 5.37 (d, J=4.95 Hz, 1H) 5.44 (s, 2H) 7.35-7.48 (m, 5H) 7.72(t, J=1.74 Hz, 1H) 7.79 (t, J=1.74 Hz, 1H) 9.26 (t, J=1.56 Hz, 1H). ¹³CNMR: δ_(C) ppm (100 MHz; DMSO-d₆) 51.88, 52.39, 62.80, 69.56, 119.53 (q,CF₃, J=321.87 Hz), 122.09, 123.76, 128.22, 129.03, 134.95, 136.81. HRMS:Calc'd for C₂₈H₃₄F₆N₅O₈S₂ [A⁺][A⁺][B⁻]: 746.1753. Found: 746.1760.Elemental Analysis: Calc'd: C, 34.67%; H, 3.35%; N, 8.18%. Found: C,35.09%; H, 3.11%; N, 7.85%. H₂O content: 483 ppm.

1,3-Bis-(2-hydroxyethyl)-imidazolium Bis(trifluoromethanesulfonimide)(Compound 13)

1-(2-hydroxyethyl)-imidazole (5.68 g, 50.7 mmol) was dissolved in CH₃CN(45 mL), then 2-bromoethanol (6.97 g, 55.8 mmol) was added and thereaction heated to reflux and stirred for 16 h. After several hours, awhite precipitate formed. The flask was then cooled, the solid filteredand washed with Et₂O (250 ml) and dried under vacuum to produce 10.51 gof a white powder. 10.00 g of this white powder were dissolved indeionized H₂O (50 mL) and LiTf₂N (13.33 g, 46.42 mmol) was added. Ayellow oil immediately formed at the bottom of the flask and reactionwas stirred for several hours at room temperature. The oil was taken upin EtOAc (200 mL) and washed with deionized H₂O (5×100 mL). The fourthand fifth aqueous washings were free of halides as confirmed lack ofprecipitate upon addition of by addition of AgNO₃. The organic phase wasdried over anhydrous MgSO₄, followed by addition of activated carbon.This mixture was filtered through basic Al₂O₃, which was washed withEtOAc (100 mL). The filtrate was concentrated, and the product driedunder vacuum at 65° C. overnight to produce 13 as a pale yellow,gel-like solid. (8.55 g, 46.3%). ¹H NMR: δ_(H) ppm (400 MHz; DMSO-d₆)3.74 (t, J=4.49 Hz, 4H) 4.15-4.32 (m, 4H) 5.17 (br. s., 2H) 7.72 (d,J=1.65 Hz, 2H) 9.10 (s, 1H).

Synthesis of Poly(RTIL) Thin Films

The styrene monomer shown in Formula 3 was synthesized as follows.Imidazole was alkylated with chloropropanediol and then treated withchloromethylstyrene to give the imidazolium chloride salt. Subsequention exchange to the Tf2N anion afforded the polymerizable RTIL monomer.When the diol-RTIL is exposed to UV light it can undergophotopolymerization (chain-addition photopolymerization) to produce apolymeric material. When this process was carried out between glassplates, a thin film was obtained.

Example 12 Water Vapor Flux Membranes Based on VicinalDiol-Functionalized Imidazolium-Based RTILS

A breathable membrane that demonstrates high water vapor flux wasprepared using a diol-functionalized polymerizable room temperatureionic liquid. A novel monomer material was synthesized and used tofabricate thin films which were tested for their ability to transportwater vapor. These materials were tested beside commercial breathablepolymers for comparison.

Introduction

Breathable fabrics that can selectively transport water vapor areimportant for both work and leisure activities. For leisure, thesematerials are used for items that allow good “breathability” forevaporative cooling but resist dirt, wind, or liquid water penetration,such as foul weather clothing, packs, gloves, rainwear, skiwear, as wellas linings and inserts for clothing. Work clothing includes survivalsuits, military protective clothing, clean room garments, wounddressings, and filtration. The materials themselves can be categorizedas closely woven fabrics, microporous membranes, hydrophilic membranesand combinations of these materials. A key parameter is a minimum watervapor flux of 0.5 kg m⁻² day⁻¹.

Various materials have been studied for water vapor transport. Nafion™is an ion-exchange membrane that has been evaluated for a variety ofapplications including fuel cells and chloro-alkali separations wherewater management is an important factor. Romero and Merida evaluatedwater transport under both water liquid-equilibrated andvapor-equilibrated conditions. They concluded that liquid equilibrationconditions were superior since the water transport rate decreasedsubstantially if the membrane-fluid interface became dry (Romero, T.; etal. J. Membrane Sci., 2009, 338, 135-144). Under vapor equilibration at30° C., the water flux was approximately 3 kg m⁻² day⁻¹. The flux didnot vary linearly with thickness, indicating the importance of theinterfacial mass transfer resistance.

Potreck et al. investigated the water vapor transport of a hydrophilic,polyethylene oxide-based block copolymer (PEBAX 1074) (Potreck, J. etal., J. Membr. Sci., 2009, 2338, 11016). The primary applications werefor dehydration of flue gas and air streams as well as natural gas dewpointing. They found that the water permeability increased exponentiallyat high water activity. They attributed this effect to swelling of thepolymer under these conditions. The water vapor flux was approximately 7kg m⁻² day⁻¹ at 30° C.

Dense polyimide membranes were evaluated for water vapor sorption andtransport by Huang et al (Huang, J. et al., J. Appl. Polym. Sci. 87,2306-2317). They studied five different polyimide materials. The bestwater transport was demonstrated using PDMA-50DDs/50ODA. Based on thepermeability and thickness values reported, their water vapor flux wasapproximately 0.030 kg m⁻² day⁻¹ at 30° C.

Block copolymers of poly(butylene terephthalate) and poly(ethyleneoxide) have also been evaluated for water transport properties (Gebben,J. Membr. Sci., 1996, 113, 323-329). The authors note that duringphysical activity, a person can evaporate 0.8 kg of water per hour,which corresponds to a heat loss of 1800 kJ. Removal of this water andheat load to the environment is a critical issue for clothing. Theirexperimental results showed a water vapor flux of approximately 2.8 kgm⁻² day⁻¹ at 30° C.

Further evidence of the importance of the water vapor transportproperties for protective clothing was provided by Li et al (Text. Res.J., 2007, 78, 1057-1069). They studied the physiological response whenwearing protective clothing. They used ten healthy adults and studiedthem wearing various protective clothing while engaging in differentactivities (treadmill exercise, working on a computer, and moving amannequin). They monitored a number of physiological parameters anddetermined that moisture transport through the clothing material was themain physiological mechanism for reduced heat stress.

The objective of this study was the synthesis of a new type of dense,hydrophilic, ionic liquid-based polymer, and the evaluation of its watervapor transport properties. This material has a thickness-normalizedwater vapor flux of 140 kg m⁻² day⁻¹ μm at 25° C., when pro-rated for amembrane thickness of 1 μm. This result is based on a 152 μm thick testmembrane film. This material offers several advantages over currentstate-of-the-art breathable materials. For example, unlike Nafion, thereis no time delay before this material reaches peak water vapor flux andit lacks pores, which precludes clogging that affects performance ofporous materials (i.e. ePTFE).

Room temperature ionic liquids (RTILs, 21, FIG. 14) are a unique classof ionic chemical compounds that are liquid at ambient temperaturebecause of a large, unsymmetrical organic cation (typically imidazoliumor ammonium) and a delocalized anion. Previous work in our labs hasfocused on polymerizable RTILs (poly(RTILs), 24, FIG. 14) used as thinfilms for gas separation applications (Carlise et al., Ind. Eng Chem.Res., 2008 (47), 7005-7012). These materials show remarkablepermeability and selectivity for light gases (CO₂, CH₄, N₂, etc.), andthe membrane properties can be tuned due to the modular nature of theRTIL monomer. Structural modifications to the monomer can change thehydrophilicity/hydrophobicity as well as the free volume of theresulting polymer. The properties of the RTIL can be easily modified byaltering the cation structure through organic synthesis or by exchangingthe anion. Polymerizable RTILs (22 and 23) are made by replacing one ofthe alkyl groups on the cation with a styrene or vinyl group.

A novel series of RTILs were recently prepared, which incorporate thecommon bis(trifluoromethanesulfonylimide) (Tf₂N) anion and a vicinaldiol-functionalized cation (LaFrate et al., Industrial and EngineeringChemistry Research (2009), 48(19), 8757-8759). Tf₂N-containing RTILs aregenerally thought of as hydrophobic and they have low water solubility(Freire, M. G. et al. J. Phys. Chem. B, 2007, 111, 13082-13089).However, these diol-functionalized RTILs (FIG. 15) showed variable watermiscibility based on the cation structure. Shorter alkyl chains on thecation (5 and 6) resulted in water soluble RTILs, while extending thealkyl chain or substituting the proton at the 2-position with a methylgroup (7-10) gave RTILs that were not water-soluble. This uniquebehavior prompted the synthesis of a polymerizable diol RTIL monomer andthe investigation of these materials for their ability to transportwater vapor.

This initial study for water vapor transport demonstrates theproof-of-concept for these materials. For future directions, RTILs haveseveral advantages for flexible design of membrane materials. As shownin FIGS. 14 and 15, different functional groups can be attached to theimidazolium cation at the 1 and 3 positions and alternate anions canalso be used to further modify the membrane properties. Variouscomposite and copolymer structures can be formed that allow for furtheradjustments in membrane permeation and mechanical properties. Due tostrong electrostatic interactions, non-polymerizable RTILs with similaror different chemical structure can be incorporated into the polymer toenhance the permeability as well as modify the physical and chemicalproperties of the membrane. These incorporated structures are stablesince they will not migrate out of the film. Solid-liquidpoly(RTIL)-RTIL composite structures have already been demonstrated forhigh permeability CO₂/N₂ separations (Bara, J. E. et al. Ind. Eng. Chem.Res., 2007, 46, 5397-5404).

Results and Discussion Synthesis

Early work involving poly(RTILs) focused on preparing styrene-basedpolymer materials (Bara, J. E. et al. Ind. Eng. Chem. Res., 2007, 46,5397-5404), so a first attempt at a polymerizable analog of thediol-functionalized RTIL was to replace the alkyl chain on the RTILcation (FIG. 15) with a styrene group (22). Imidazole was alkylated with1-chloro-2,3-propanediol in the presence of KOH and KI, to give 31(Scheme 7), which was then quaternized with chloromethylstyrene andion-exchanged to give the Tf₂N salt, 32. Autopolymerization of monomer32 was a major problem, and several batches were lost, at which pointBHT (a radical scavenger) began to be added to the product to curb thisproblem. It is also worth noting that the yield for this reaction wasconsistently quite low. Due to these issues, an alternative synthesisthat incorporated a different polymerizable group on the RTIL cation wassought to be developed.

The most logical replacement for the styrene was a vinyl group (34).1-Vinylimidazole is inexpensive, commercially available, and generallymore robust and less prone to autopolymerization. It is also convenientthat the polymerizable group is already present on the cation precursor,which streamlines the synthesis by eliminating one of the alkylationsteps. Vinylimidazole was alkylated with 1-chloro-2,3-propanediol bystirring the neat (solvent-free) reaction at 100° C. for 2 days toafford 33 (Scheme 8). This reaction can be easily monitored by thinlayer chromatography (TLC) because vinylimidazole absorbs UV and is thelimiting reagent in the reaction. After all of the starting material wasconsumed by TLC, the chloride salt product was precipitated from etherand washed several times with organic solvents to remove impurities.Chloride salt 33 was ion exchanged with LiTf₂N to give 34 in 80% overallyield. Not only is this product produced in higher yield and fewer stepsthan the styrene analog 32, it is much more stable and does not undergoautopolymerization. Monomer 34 can be heated to excess of 150° C.,exposed to ambient light and is also less viscous than the styrenemonomer, making it much easier to transfer. Small batches (10-30 g) ofvinyl monomer 34 could be further purified using dry column vacuumchromatography (DCVC) (Pedersen, D. S.; Synthesis, 2001, 16, 2431-2434),to afford very pure monomer.

Membrane Fabrication

Thin-film poly(diol-RTIL) membranes were prepared using monomer 34 witha commonly used procedure (Bara, J. E. et al. J. Membrane Sci., 2008,321, 3-7). The resulting films were optically clear and mechanicallyrobust when a cross-linker was employed (FIG. 16 shows the monomer andresulting polymer). Membranes that were used for water transport testingwere made using a support material without crosslinker. It was foundthat crosslinking provided mechanical stability to the membrane but alsodramatically reduced its water transport properties (see below).Membranes that were tested for water vapor transport were supported on apolysulfone (Supor®) material to improve mechanical stability. Themonomer was mixed with photoinitiator and poured onto the support andpressed between quartz plates and polymerized under UV light. Thesupported membranes ranged in thickness from 140 to 160 μm (calipermethod). A detailed protocol for membrane fabrication follows in thesection labeled Supporting Information.

Water Vapor Transport Testing

Many different methods have been used to test water transport, fromcomplex cross-flow systems using a carrier gas to simple human trials inthe field. A straight-forward method was chosen whereby the drivingforce for water vapor transportis a constant relative humidity (RH)differential. A test cell is filled with water and covered with themembrane material to be tested (or left open as a control) and paced inan arid environment (dessicator or glove box). The relative humidity inthe cell is high (□90% RH), and water vapor migrates across the membraneinto the dry air (1-5% RH).

Initial tests focused on the dessicator method, which worked very wellfor smaller sample sets. Cells were placed in a dessicator filled withactivated DriRite desiccant, and humidity was monitored using an analoghumidity gauge. When more than six cells were placed in the dessicatorfor testing, the relative humidity in the dessicator would increase fromless than 5% to over 20%. Because it is a static system, equilibrium isreached when the DrieRite dessicant becomes partially saturated. Forlarger scale experiments, an alternate method was employed which uses aconstant flow of dry N₂ gas in a portable glovebox (containing desiccantand a balance) to carry away humid air. It is imperative that relativehumidity outside the cells remains constant, since it provides thedriving force for the experiment and could lead to discrepancies inwater vapor flux through the membrane. Using this glovebox method,humidity remained constant (1% RH) over the course of the experiment,even with 15 test cells present. The glovebox method is advantageousover the dessicator because the cells remain in the test environment forthe entire experiment (even during weighing). Detailed procedures forboth methods of water vapor transport testing can be found in thesupporting information. Flux values, which represent the amount of watervapor moving across a given area of membrane over time, can be easilycalculated from this data and used to compare membrane performance.

Several basic experiments were conducted using the dessicator watervapor transport testing method to examine important factors that mightaffect membrane performance and to determine key structure-propertyrelationships. Data plots from these experiments can be found in thesupporting information. The effect of monomer purity on membraneperformance was investigated first. Supported membranes were preparedusing monomer 34 at various levels of purity (crude, semi-pure and pure)under identical processing conditions and then tested simultaneously.Removal of major impurities by liquid-liquid extraction and stirringwith activated charcoal gave a semi-pure membrane that showed 10% higherwater vapor flux than the crude material. Further purification of 34 byDCVC, resulted in a film that had 3% higher flux than the semi-crudeanalog. These differences in flux can be attributed to copolymerizationof impurities which disrupt the continuous diol-RTIL network in thepolymer, which is responsible for water vapor transport. For thisreason, the purest form of monomer 34 was used for all future membranefabrication. However, the performance difference between the semi-crudeand pure product is small (3%), so for large-scale applications theexpensive and time-consuming column chromatography purification could beeliminated with minimal effect on membrane transport function.

Because a supported membrane system is being employed, it is importantto test the support material without any poly(diol-RTIL) present toensure that the polymer material, not the support, is facilitating watervapor transport. Unsupported poly(diol-RTIL) films were also prepared totest the opposite effect. When the 100-μm polysulfone (Supor) supportwas tested using the dessicator method, its flux was 5% lower than thatof an open cell in the same data set, while thesupported-poly(diol-RTIL) membrane flux was 13% lower than the blank.This shows that the Supor support provides minimal resistance to themovement of water vapor. In a similar test, supported and unsupportedpoly(diol-RTIL) films showed nearly identical flux values when testedside by side, indicating that the poly(diol-RTIL) is responsible forwater vapor transport.

Finally, the effect of polymer cross-linking on membrane performance wasexamined. Poly(diol-RTIL) films were fabricated under similar conditionswith varying amounts of crosslinker (0, 5 and 10 mol %). The membranethat contained 5 mol % cross-linker had 35% lower water vapor flux thanthe pure poly(diol-RTIL) film. Increasing the cross-linker concentrationfrom 5 to 10 mol % resulted in a 36% decrease in flux. This result isexpected because the cross-linker effectively tightens the polymernetwork in the membrane and subsequently causes an increase inresistance to water vapor permeability.

With a basic understanding of membrane performance andstructure-property relationships, the water vapor transport propertiesof the poly(diol-RTIL) films was tested alongside commercial breathablepolymers. Initial tests were conducted using the dessicator method,however due to the large number of test cells and increased amount ofwater evaporating, the humidity in the dessicator increased over thecourse of the experiment. This caused the flux values to decrease overtime as the humidity increased. To solve this problem, an alternativemethod was sought which used a carrier gas to sweep away the humid air.A test procedure using a glove box worked well and humidity stayedconstant for the entire experiment. The results from this experiment arepresented in FIG. 17 and Table 10.

TABLE 10 Water vapor transport results from glovebox test. Membranethickness, water uptake after 12.5 h experiment, flux andthickness-normalized flux to 1 μm. Water Flux Thickness- ThicknessUptake (kg m⁻² Normalized Flux Membrane (μm) (wt %) day⁻¹) (kg m⁻² ·day⁻¹ μm) Poly(diol-RTIL) 152 2.6 0.937 142 (35) Nafion117 178 4.4 1.36243 ePTFE N/A −13 1.12 N/A Omniflex ® N/A 0 1.13 N/A Blank N/A N/A 1.49N/A

The poly(diol-RTIL) membrane fabricated from DCVC-purified monomer 34was tested simultaneously with other commercial breathable materials:Nafion-117, porous ePTFE, and Omniflex®, and also compared with an opencell without any membrane present (FIG. 17, Table 10). Nafion-117 is adense, highly acidic, ionic fluoropolymer produced by DuPont, and isused mainly in fuel cell applications. Porous poly(tetraflouroethylene)(ePTFE) is a polymer that is used to make Gore-Tex®, a well-knowncommercial material that efficiently transports water vapor. Omniflex®is a porous polyurethane film made by Argotech that is used mainly forrecreational outdoor clothing.

As can be seen in FIG. 17 and Table 10, Nafion-117 showed the higheststeady state flux of all the membranes under these test conditions. Itis worth noting that the Nafion membrane's performance increaseddramatically after several hours. Nafion-117 transports water vapor mosteffectively when the polymer is hydrated, which causes the material toswell and water vapor flux to increase. The membranes were weighedbefore and after the transport test and Nafion showed the largestaverage water uptake at 4.4 wt % after 12.5 h, while the poly(diol-RTIL)only absorbed 2.6 wt % water and the flux remained steady. Curiously,the ePTFE membrane lost mass (13 wt %) over the course of theexperiment. Often Gore-Tex® and other ePTFE-based materials are coatedwith a polyurethane material that helps prevent clogging of pores withsweat, dirt and other debris. It is possible that this coating wasdissolved by water during testing, resulting in a lower membrane mass.

Both of the porous materials, ePTFE and Omniflex®, performed slightlyworse than Nafion-117 under these conditions. The water vapor transportof these materials depends on the number and size of pores in the filmand is limited by their maximum density. Because the transport mechanismis quite different from that of a dense film like Nafion or thepoly(diol-RTIL), it is difficult to make performance comparisons. Thesematerials were included because they are common commercial materials,but their use is mainly limited to recreational outdoor clothing andaccessories.

The poly(diol-RTIL) had lower flux than all of the commercial membranesbut is still quite breathable with a flux of nearly 1 kg H₂O vapor persquare meter of material per day. When the membrane performance isnormalized for thickness from 152 μm to 1 μm, the thickness-normalizedwater vapor flux is over 140 kg m⁻² day⁻¹ μm. This value is orders ofmagnitude greater than the ideal value of 0.5 kg m⁻²-day⁻¹ μm given byMukhopadhyay et al (J. Ind. Text. 2008, 37, 225-262), so the utility ofthis material as a breathable film is still viable. Furthermore, thepoly(diol-RTIL) films offer several advantages over the commercialbreathable membranes. Unlike Nafion, which is also a dense filmmaterial, the poly(diol-RTIL) membrane exhibits no “time-lag” to reachpeak flux and is also more flexible, making is more amenable toprotective clothing applications. The poly(diol-RTIL) material lackspores, so unlike ePTFE and Omniflex®, its performance cannot becompromised by clogging of the pores. Poly(RTILs) are modular by natureand the monomer can easily be modified through organic synthesis to tunemembrane properties. The transport properties can be fine tuned byforming co-polymers or composites with other RTIL-based compounds, whichis not possible with these commercial materials.

The mechanism for water vapor transport is thought to involve the diolfunctionality on the poly(RTIL) cation. A control membrane was preparedusing a relatively hydrophobic RTIL monomer ([Hvim][Tf₂N], 23, FIG. 14)with an alkyl chain in place of the diol moiety. This membrane had awater vapor flux of 0.081 kg m⁻²·day⁻¹, while the poly(diol-RTIL)membrane flux was 1.240 kg m⁻²·day⁻¹ under identical conditions. The“traditional” poly(RTIL) shows a low level of water transport which maybe attributed to the ionic nature of the polymer, but the flux increasesby over 15-fold when the n-hexyl group is replaced with the diol. Theproposed transport mechanism relies on hydrogen-bonding between the dioloxygens on the RTIL cation and one of the water molecule's protons. Thisallows the water to interact favorably with the polymer chain and to beabsorbed into the membrane. Once in the polymer matrix, water moleculescan shuttle from one diol group to the next, eventually making their wayacross the membrane.

Conclusions

A novel, water-vapor-breathable, dense thin film material was preparedbased on a diol-functionalized, polymerizable RTIL, 34. The basicstructure-property relationships of this poly(diol-RTIL) in the form ofsupported membranes were examined, and it was found that polymercrosslinking decreased membrane performance. Tests were performed toconfirm that the diol-RTIL polymer component of the supported membraneis responsible for transporting water. Although the poly(diol-RTIL)films did not perform as well as some commercial high water vaportransport membranes, they offer several advantages to these materials.The poly(diol-RTIL) membranes tested here are relatively thick (˜150μm), so the production of thinner films should lead to enhanced absoluteperformance. Other RTIL-based monomers inspired by monomer 34 may beprepared with alternate cation substitution and different anions andtheir membrane morphology studied using a variety of methods to helpelucidate the mechanism of water transport. Another focus ispoly(RTIL)/RTIL composite materials which showed significant increase inpermeability of light gases and may enhance water vapor transportcompared to poly(RTILs).

Supporting Information General Considerations

All reagents were purchased from reputable commercial suppliers(Aldrich, TCI America and 3M) and were used without furtherpurification. Supor® (polysulfone support material) was purchased fromPall, Inc (Ann Arbor, Mich.). UHP grade N₂ was used for water transporttests conducted using the glove box method. ¹H NMR spectra were recordedon a 300 MHz Varian instrument and ¹³C NMR were recorded at 75 MHz onthe same instrument. NMR spectra are reported in ppm and were referencedto the solvent peak and were processed using MestReNova (v. 5.3.3)software. ESI mass spectra were recorded using the Applied BiosystemsQSTAR Hybrid LC/MS/MS System mass spectrometer. A UVP Inc. CL-1000Ultraviolet Crosslinker was used to conduct polymerization reactions.

Experimental Monomer Synthesis 1-(2,3-Dihydroxypropyl)-imidazole (31)

Imidazole (3.40 g, 50.0 mmol), pulverized potassium hydroxide (5.61 g,100 mmol), and potassium iodide (8.30 g, 50.0 mmol) were suspended inCH₃CN (100 mL). 3-Chloro-1,2-propanediol (8.29 g, 75.0 mmol) was added,and the mixture was stirred at reflux for 24 h. After cooling to roomtemperature, additional CH₃CN (150 mL) was added to the reaction, whichwas then filtered through Celite and concentrated. The crude product wasthen suspended in CH₂Cl₂ (250 mL), heated to reflux and stirredovernight, and then decanted. The product was still slightly impure by¹H NMR, so the CH₂Cl₂ wash process was repeated once, to afford a whitesolid (6.82 g, 96%) after drying in vacuo. ¹H NMR (400 MHz, DMSO) δ 7.54(t, J=1.0 Hz, 1H), 7.11 (t, J=1.2 Hz, 1H), 6.84 (t, J=1.0 Hz, 1H), 5.08(s, 1H), 4.83 (s, 1H), 4.05 (dd, J=13.9, 3.6 Hz, 1H), 3.84 (dd, J=14.0,7.2 Hz, 1H), 3.70-3.58 (m, 1H), 3.31 (dt, J=13.8, 9.0 Hz, 3H), 3.19 (dd,J=11.0, 6.5 Hz, 1H).

1-(2,3-Dihydroxypropyl)-3-(p-styryl)-imidazoliumBis(trifluoromethanesulfonimide) (32)

1-(2,3-Dihydroxypropyl)-imidazole (31, 6.80 g, 48 mmol) was partiallydissolved in CH₃CN (200 mL) with heating. Chloromethylstyrene (10.2 mL,72.0 mmol) was added and the reaction was stirred at 65° C. for 20 h.After cooling, the mixture was partially concentrated and poured intoEt₂O (500 mL), generating a white precipitate. The precipitate wasdissolved in H₂O (200 mL) and washed with Et₂O (2×100 mL), then EtOAc(2×100 mL) and finally CH₂Cl₂ (2×100 mL). LiTf₂N (20.6 g, 72.0 mmol) wasadded to the water layer, and the mixture was stirred overnight. Aseparate phase formed, which was extracted into CH₂Cl₂ (2×150 mL),washed with H₂O (5×100 mL), and then dried over MgSO₄, filtered andconcentrated. A few grains of BHT were mixed into the final product toprevent unwanted radical autopolymerization. The product was an orangeoil (3.72 g, 14%). ¹H NMR (400 MHz, DMSO) δ 9.24 (t, J=1.4 Hz, 1H), 7.78(t, J=1.8 Hz, 1H), 7.72 (t, J=1.8 Hz, 1H), 7.53 (d, J=8.2 Hz, 2H), 7.40(d, J=8.2 Hz, 2H), 6.74 (dd, J=17.7, 11.0 Hz, 1H), 5.43 (s, 2H), 5.37(d, J=5.2 Hz, 1H), 5.30 (dd, J=10.9, 0.8 Hz, 1H), 4.96 (t, J=5.5 Hz,1H), 4.32 (dd, J=13.8, 3.0 Hz, 1H), 4.10 (dd, J=13.8, 8.0 Hz, 1H),3.83-3.74 (m, 1H), 3.44 (dt, J=10.3, 5.1 Hz, 1H), 3.30-3.21 (m, 1H).

1-(2,3-Dihydroxypropyl)-3vinylimidazoliumBis(trifluoromethanesulfonimide) (34)

1-Vinylimidazole (47.1 g, 500 mmol) and 1-chloro-2,3-propanediol (126mL, 1500 mmol) were combined in a flask and heated to 100° C. for 48 h,at which point the reaction was complete by TLC (eluant: 10%CH₃OH/EtOAc). After cooling to room temperature, the mixture was pouredinto Et₂O (2.5 L) and stirred vigorously at ambient temperature for 4 h.The product was then scraped from the sides of flask and broken up withspatula. EtOAc (2 L) was then added, and the mixture stirred for 6 hourswith periodic gentle heating using a heat gun. The EtOAc was decantedand fresh EtOAc (1.5 L) was added, stirred overnight and decanted. ¹HNMR of the crude chloride salt showed some impurities, so it wasdissolved in H₂O (500 mL) and washed with CH₂Cl₂ (4×100 mL) and thenEtOAc (6×100 mL). LiTf₂N (158 g, 550 mmol) was added to the H₂O layerand stirred overnight. A separate layer formed, which was extracted intoEtOAc (2×300 mL) and washed with H₂O (6×100 mL), dried over MgSO₄ andfiltered. Activated carbon was added to the EtOAc solution, and theresulting mixture was stirred for 2 days, then filtered through Celite,and finally concentrated to give the product as an orange oil (180 g,80%). Small batches (20-40 g) were purified using the dry column vacuumchromatography method described by Pedersen and Rosenbohm (Synthesis,2001, 16, 2431-2434) using gradient elution from 2.5% MeOH/CHCl₃ to 20%MeOH/CH₂Cl₂ to afford quite pure product. The amount of MeOH wasincreased by 2.5% after each 100 mL fraction of eluent. When 20%MeOH/CHCl₃ was reached, the solvent was switched to 20% MeOH/CH₂Cl₂. ¹HNMR (300 MHz, DMSO) δ 9.42 (t, J=1.5 Hz, 1H), 8.18 (t, J=1.8 Hz, 1H),7.84 (t, J=1.7 Hz, 1H), 7.33 (dd, J=15.7, 8.8 Hz, 1H), 5.96 (dd, J=15.7,2.4 Hz, 1H), 5.42 (dd, J=8.8, 2.4 Hz, 2H), 4.97 (s, 1H), 4.34 (dd,J=13.7, 3.0 Hz, 1H), 4.10 (dd, J=13.8, 8.2 Hz, 1H), 3.89-3.69 (m, 1H),3.61-3.06 (m, 6H). ¹³C NMR (75 MHz, DMSO) δ 135.97, 128.85, 124.20,119.53 (q, CF₃, J=321.8 Hz), 118.58, 108.55, 69.51, 62.76, 52.70. MS:m/z=169.1 (cation, C₈H₁₄N₂O₂ ⁺). CHN elemental analysis of the compoundwas attempted but the compounds did not burn cleanly (often observedwith RTILs with Tf₂N anion), so copies of ¹H and ¹³C NMR spectra of themonomer are included in this supporting information in lieu of elementalanalysis for purity.

Supported Membrane Fabrication

Monomer 34 was mixed with photoinitiator (2-hydroxypropiophenone, 2 wt%) using a vortexer and poured onto a 250-mm diameter Supor® (100 μmpolysulfone) support material. The monomer on support was then pressedbetween two quartz plates covered with Rain-X (commercial hydrophobic,anti-stick coating for glass) to prevent sticking. After manuallypressing to remove bubbles, the plates were clipped together usingbinder clips and placed in a UV oven (UVP Inc., CL-1000 UltravioletCrosslinker) and polymerized for 4 h at 0.15 J/cm² power setting andflipped halfway through. The membrane was scraped from the platescarefully using a razorbiade. The thickness of each membrane wasmeasured using a caliper micrometer. All supported membranes hadthicknesses of 140-160 μm. Membranes were stored between Parafilm sheets(to prevent sticking) in plastic bags. Unsupported membranes wereprepared in a similar fashion, but with the monomer poured directly ontothe Rain-X coated quartz plates.

Water Vapor Transport Testing

Membrane samples were cut using a 25-mm sharpened punch die. Themembranes were then placed in a 15-mm I.D. PVC cell made frominexpensive parts available at a hardware store. One end of a plumbingunion was plugged using a hollow PVC bolt, while the other end was leftopen. The membrane was placed in the middle of the union, seated on ano-ring. The union was joined and placed on the bench top. One hand wasplaced on top on the cell and used to press down firmly, while screwingon the union collar, so as not to torque the membrane. In someexperiments, one cell was left blank (i.e. open, without any membrane inplace) for use as a control to demonstrate maximum water transportwithout any sample in the transport path. The same test cell set up wasused for all experiments, however two different methods were used fortesting water vapor transport.

Desiccator Method

The cells were weighed and then placed in a medium-sized dessicatorcontaining DriRite dessicant (454 g), which was placed in a 120° C.overnight to ensure dryness. The dessicator was sealed and humidity wasmonitored using an analog hygrometer. The cells were removed from thedessicator and weighed periodically. Intervals of less than 12 hourswere avoided to prevent error from opening and closing the dessicatorwhich could cause humidity fluctuations. The mass of water lost fromeach cell was plotted against time and used to calculate the membraneflux.

This method worked well for sample sets of six or less, however, whenmore than six cells were placed in the dessicator the relative humiditywould gradually increase from less than 5% to over 20% over the courseof the experiment. With that much water vapor present in a closedsystem, the humidity increases until an equilibrium is reached. Humidityfluctuations are detrimental to the experiment because the difference inrelative humidity between the inside of the cell and the dessicator arethe driving force for the experiment. When larger sample sets wererequired a glove box with nitrogen flow (to sweep away humid air) wasemployed. The absolute flux numbers for a sample are different under thedessicator and glove box conditions, but the relative values betweensamples are consistent.

Glove Box Method

The cells were placed in a portable acrylic glove box connected to a N2tank maintained at constant output pressure with two-stage pressureregulator connected to the tank. A diffuser tube was made by pluggingone end of a foot-long piece of Tygon tubing and poking several holes inthe tube. A windscreen was made using glass plates to block the cellsfrom air flow and to prevent air currents from introducing experimentalerror. A balance and container of DrieRite (dessicant) were placed inthe glove box and it was purged for one hour at 10 psi N2. The flow wasthen turned down to 4 psi and the cells were weighed periodically. Themass of water lost from each cell was plotted against time and used tocalculate the membrane flux where

${Flux} - \frac{{mass}\mspace{14mu} {loss}}{\left( {{surface}\mspace{14mu} {area}} \right) \times ({time})}$

See also LaFrate et al., Ind. Eng. Chem. Res., Article ASAP; DOI:10.1021/ie100227h, 2010, hereby incorporated by reference.

Having now fully described the present invention in some detail by wayof illustration and examples for purposes of clarity of understanding,it will be obvious to one of ordinary skill in the art that the same canbe performed by modifying or changing the invention within a wide andequivalent range of conditions, formulations and other parameterswithout affecting the scope of the invention or any specific embodimentthereof, and that such modifications or changes are intended to beencompassed within the scope of the appended claims.

One of ordinary skill in the art will appreciate that startingmaterials, reagents, purification methods, materials, substrates, deviceelements, analytical methods, assay methods, mixtures and combinationsof components other than those specifically exemplified can be employedin the practice of the invention without resort to undueexperimentation. All art-known functional equivalents, of any suchmaterials and methods are intended to be included in this invention. Theterms and expressions which have been employed are used as terms ofdescription and not of limitation, and there is no intention that in theuse of such terms and expressions of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed. Thus, it should be understood that although thepresent invention has been specifically disclosed by preferredembodiments and optional features, modification and variation of theconcepts herein disclosed may be resorted to by those skilled in theart, and that such modifications and variations are considered to bewithin the scope of this invention as defined by the appended claims.

As used herein, “comprising” is synonymous with “including,”“containing,” or “characterized by,” and is inclusive or open-ended anddoes not exclude additional, unrecited elements or method steps. As usedherein, “consisting of” excludes any element, step, or ingredient notspecified in the claim element. As used herein, “consisting essentiallyof” does not exclude materials or steps that do not materially affectthe basic and novel characteristics of the claim. In each instanceherein any of the terms “comprising”, “consisting essentially of” and“consisting of” may be replaced with either of the other two terms.

When a group of materials, compositions, components or compounds isdisclosed herein, it is understood that all individual members of thosegroups and all subgroups thereof are disclosed separately. When aMarkush group or other grouping is used herein, all individual membersof the group and all combinations and subcombinations possible of thegroup are intended to be individually included in the disclosure. Everyformulation or combination of components described or exemplified hereincan be used to practice the invention, unless otherwise stated. Whenevera range is given in the specification, for example, a temperature range,a time range, or a composition range, all intermediate ranges andsubranges, as well as all individual values included in the ranges givenare intended to be included in the disclosure. In the disclosure and theclaims, “and/or” means additionally or alternatively. Moreover, any useof a term in the singular also encompasses plural forms.

All references cited herein are hereby incorporated by reference intheir entirety to the extent that there is no inconsistency with thedisclosure of this specification. Some references provided herein areincorporated by reference to provide details concerning sources ofstarting materials, additional starting materials, additional reagents,additional methods of synthesis, additional methods of analysis,additional biological materials, additional peptides, chemicallymodified peptides, additional cells, and additional uses of theinvention. All headings used herein are for convenience only. Allpatents and publications mentioned in the specification are indicativeof the levels of skill of those skilled in the art to which theinvention pertains, and are herein incorporated by reference to the sameextent as if each individual publication, patent or patent applicationwas specifically and individually indicated to be incorporated byreference. References cited herein are incorporated by reference hereinin their entirety to indicate the state of the art as of theirpublication or filing date and it is intended that this information canbe employed herein, if needed, to exclude specific embodiments that arein the prior art. For example, when composition of matter are claimed,it should be understood that compounds known and available in the artprior to Applicant's invention, including compounds for which anenabling disclosure is provided in the references cited herein, are notintended to be included in the composition of matter claims herein.

1-52. (canceled)
 53. A composition comprising: (a) a polymerizedroom-temperature ionic liquid (RTIL) comprising a plurality ofRTIL-based repeating units of general formula:

wherein: R₁ is selected from the group consisting of hydrogen andoptionally substituted branched and unbranched alkyl, alkenyl, alkynyl,and aryl groups having 1 to 20 carbon atoms; R₂ is selected from thegroup consisting of a bond and optionally substituted branched andunbranched alkylene, alkenylene, alkynylene, and arylene groups having 1to 12 carbon atoms, X₁ is an anion, Z₁, Z₂ and Z₃ are independentlyselected from the group consisting of hydrogen and optionallysubstituted branched and unbranched alkyl, alkenyl, alkynyl, and arylgroups having 1 to 12 carbon atoms, and the number of repeating units inthe RTIL polymer is from 2 to 100,000; and, (b) an unpolymerized RTIL offormula:

wherein: R₃ and R₄ are independently selected from the group consistingof optionally substituted branched and unbranched alkyl, alkenyl,alkynyl, and aryl groups having 1 to 20 carbon atoms, X₂ is an anion, Yis selected from the group consisting of hydrogen and optionallysubstituted branched and unbranched alkyl, alkenyl, and alkynyl groupshaving 1 to 12 carbon atoms, Z₄ and Z₅ are independently selected fromthe group consisting of hydrogen, and optionally substituted branchedand unbranched alkyl, alkenyl, and alkynyl groups having 1 to 12 carbonatoms; wherein the unpolymerized RTIL is between 5 mol % to 60 mol % ofthe total RTIL of the composition, and wherein at least one of R₁, R₃ orR₄ is substituted with at least one hydroxyl group.
 54. The compositionof claim 53, wherein Y, Z, Z₂, Z₃, Z₄, and Z₅ are independently selectedfrom the group consisting of hydrogen and optionally substitutedbranched and unbranched alkyl groups having 1 to 4 carbon atoms.
 55. Thecomposition of claim 53, wherein Y is hydrogen or methyl, and Z₁, Z₂,Z₃, Z4, and Z₅ are hydrogen.
 56. (canceled)
 57. The composition of claim53, wherein the polymerized RTIL is:


58. The composition of claim 53, wherein R₁, R₃ and R₄ are independentlyselected from the group consisting of optionally selected branched andunbranched alkyl, alkenyl, alkynyl, and aryl groups having 1 to 10carbon atoms.
 59. The composition of claim 53, wherein R₁ is


60. The composition of claim 53, wherein the polymerized RTIL comprises:

where X⁻ is an anion selected from the group consisting of abistrifluoromethylsulfonyl)imide ion (Tf₂N⁻), a halide ion, ahexafluorophosphate ion (PF₆ ⁻), a tetrafluoroborate ion (BF₄ ⁻), adicyanamide ion (N(CN)₂ ⁻), a sulfonated ion and a fluorinatedsulfonated ion.
 61. The composition of claim 53, wherein theunpolymerized RTIL is:


62. The composition of claim 53, wherein between 10 mol % to 35 mol % ofthe total RTIL of the composition is unpolymerized RTIL.
 63. A membranecomprising a first layer and an opposing second layer, the first andsecond layers each comprising a polymerized RTIL, wherein anunpolymerized RTIL is between the first and second layers, wherein thepolymerized RTIL comprises a plurality of RTIL-based repeating units ofgeneral formula:

wherein: R₁ is selected from the group consisting of hydrogen andoptionally substituted branched and unbranched alkyl, alkenyl, alkynyl,and aryl groups having 1 to 20 carbon atoms; R₂ is selected from thegroup consisting of a bond and optionally substituted branched andunbranched alkylene, alkenylene, alkynylene, and arylene groups having 1to 12 carbon atoms, X₁ is an anion, Z₁, Z₂ and Z₃ are independentlyselected from the group consisting of hydrogen and optionallysubstituted branched and unbranched alkyl, alkenyl, alkynyl, and arylgroups having 1 to 12 carbon atoms, and the number of repeating units inthe RTIL polymer is from 2 to 100,000; and wherein the unpolymerizedRTIL is:

wherein: R₃ and R₄ are independently selected from the group consistingof optionally substituted branched and unbranched alkyl, alkenyl,alkynyl, and aryl groups having 1 to 20 carbon atoms, X₂ is an anion, Yis selected from the group consisting of hydrogen and optionallysubstituted branched and unbranched alkyl, alkenyl, and alkynyl groupshaving 1 to 12 carbon atoms, Z₄ and Z₅ are independently selected fromthe group consisting of hydrogen and optionally substituted branched andunbranched alkyl, alkenyl, and alkynyl groups having 1 to 12 carbonatoms; wherein the unpolymerized RTIL is between 5 mol % to 60 mol % ofthe total RTIL comprised in or on the membrane, and wherein at least oneof R₁, R₃ or R₄ is substituted with at least one hydroxyl group.
 64. Themembrane of claim 63, wherein the membrane has a CO₂ permeabilityranging from 16 to 44 barrers.
 65. The membrane of claim 63, wherein themembrane has a carbon dioxide/methane (CO₂/CH₄) separation selectivityof 37 or greater.
 66. The membrane of claim 63, wherein the membrane hasa carbon dioxide/nitrogen (CO₂/N₂) separation selectivity of 40 orgreater.
 67. The membrane of claim 63, wherein the thickness of themembrane ranges is from 50 nm to 200 μm.
 68. A method for separating afirst gas component from a gas mixture comprising at least a first and asecond gas component, the method comprising the steps of: (a) providinga membrane having a feed and a permeate side and being selectivelypermeable to the first gas component over the second gas component; (b)applying a feed stream including the first and the second gas componentsto the feed side of the membrane; and (c) providing a driving forcesufficient for permeation of the first gas component through themembrane, thereby producing a permeate stream enriched in the first gascomponent from the permeate side of the membrane; wherein the membranecomprises: (i) a polymerized room-polymerized ionic liquid (RTIL)comprising a plurality of RTIL-based repeating units of general formula:

wherein: R₁ is selected from the group consisting of hydrogen andoptionally substituted branched and unbranched alkyl, alkenyl, alkynyl,and aryl groups having 1 to 20 carbon atoms; R₂ is selected from thegroup consisting of a bond and optionally substituted branched andunbranched alkylene, alkenylene, alkynylene, and arylene groups having 1to 12 carbon atoms, X₁ is an anion, Z₁, Z₂ and Z₃ are independentlyselected from the group consisting of hydrogen and optionallysubstituted branched and unbranched alkyl, alkenyl, alkynyl, and arylgroups having 1 to 12 carbon atoms, and the number of repeating units inthe RTIL polymer is from 2 to 100,000; and (ii) unpolymerized RTIL offormula:

wherein: R₃ and R₄ are independently selected from the group consistingof optionally substituted branched and unbranched alkyl, alkenyl,alkynyl, and aryl groups having 1 to 20 carbon atoms, X₂ is an anion, Yis selected from the group consisting of hydrogen and optionallysubstituted branched and unbranched alkyl, alkenyl, and alkynyl groupshaving 1 to 12 carbon atoms, Z₄ and Z₅ are independently selected fromthe group consisting of hydrogen, and optionally substituted branchedand unbranched alkyl, alkenyl, and alkynyl groups having 1 to 12 carbonatoms; wherein the unpolymerized RTIL is between 5 mol % to 60 mol % ofthe total RTIL of the composition, and wherein at least one of R₁, R₃ orR₄ is substituted with at least one hydroxyl group.
 69. The method ofclaim 68, wherein the first gas component is carbon dioxide (CO₂) andthe second gas component is methane (CH₄).
 70. The method of claim 68,wherein the first gas component is carbon dioxide (CO₂) and the secondgas component is nitrogen gas (N₂).
 71. The method of claim 68, whereinthe thickness of the membrane ranges from 50 nm to 200 μm.
 72. Themethod of claim 68, wherein the membrane has a carbon dioxide/methaneseparation selectivity of at least 20 or a carbon dioxide/nitrogen gasseparation selectivity of at least 32.